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Sun, 18 Mar 2018

Showing 254 entries from Fri, 09 Mar 2018 to Thu, 15 Mar 2018

Submitted Thu, 15 Mar 2018

[1] arXiv:1803.05901v1 [pdf, vox]

Neutrino tomography of the Earth

Andrea Donini, Sergio Palomares-Ruiz, Jordi Salvado
Submitted Thursday 15 March 2018 @ 17:59:12 GMT
16 pages, 10 figures and 1 table

Cosmic-ray interactions with the nuclei of the Earth's atmosphere produce a flux of neutrinos in all directions with energies extending above the TeV scale. However, the Earth is not a fully transparent medium for neutrinos with energies above a few TeV. At these energies, the charged-current neutrino-nucleon cross section is large enough so that the neutrino mean-free path in a medium with the Earth's density is comparable to the Earth's diameter. Therefore, when neutrinos of these energies cross the Earth, there is a non-negligible probability for them to be absorbed. Since this effect depends on the distance traveled by neutrinos and on their energy, studying the zenith and energy distributions of TeV atmospheric neutrinos passing through the Earth offers an opportunity to infer the Earth's density profile. Here we perform an Earth tomography with neutrinos using actual data, the publicly available one-year through-going muon sample of the atmospheric neutrino data of the IceCube neutrino telescope. We are able to determine the mass of the Earth, its moment of inertia, the mass of the Earth's core and to establish the core is denser than the mantle, using weak interactions only, in a way completely independent from gravitational measurements. Our results confirm that this can be achieved with current neutrino detectors. This method to study the Earth's internal structure, complementary to the traditional one from geophysics based on seismological data, is starting to provide useful information and it could become competitive as soon as more statistics is available thanks to the current and larger future neutrino detectors.

[2] arXiv:1803.05898v1 [pdf, vox]

Effects of a subadiabatic layer on convection and dynamos in spherical wedge simulations

Petri J. Käpylä, Mariangela Viviani, Maarit J. Käpylä, Axel Brandenburg
Submitted Thursday 15 March 2018 @ 17:53:28 GMT
22 pages, 9 figures, submitted to GAFD

We consider the effect of a subadiabatic layer at the base of the convection zone on convection itself and the associated large-scale dynamos in spherical wedge geometry. We use a heat conduction prescription based on the Kramers opacity law which allows the depth of the convection zone to dynamically adapt to changes in the physical characteristics such as rotation rate and magnetic fields. We find that the convective heat transport is strongly concentrated toward the equatorial and polar regions in the cases without a substantial radiative layer below the convection zone. The presence of a stable layer below the convection zone significantly reduces the anisotropy of radial enthalpy transport. Furthermore, the dynamo solutions are sensitive to subtle changes in the convection zone structure. We find that the kinetic helicity changes sign in the deeper parts of the convection zone at high latitudes in all runs. This region expands progressively toward the equator in runs with a thicker stably stratified layer.

[3] arXiv:1803.05892v1 [pdf, vox]

Afterglow Imaging and Polarization of Misaligned Structured GRB Jets and Cocoons: Breaking the Degeneracy in GRB 170817A

Ramandeep Gill, Jonathan Granot
Submitted Thursday 15 March 2018 @ 17:46:08 GMT
14 pages, 9 figures, submitted to MNRAS

The X-ray to radio afterglow emission of GRB 170817A/GW 170817 so far scales as $F_\nu\propto\nu^{-0​.6}t^{0.8}$ with observed frequency and time, consistent with a single power-law segment of the synchrotron spectrum from the external shock going into the ambient medium. This requires the effective isotropic equivalent afterglow shock energy in the visible region to increase as $\sim t^{1.7}$. The two main channels for such an energy increase are (i) \emph{radial}: more energy carried by slower material (in the visible region) gradually catches up with the afterglow shock and energizes it, and (ii) \emph{angular}: more energy in relativistic outflow moving at different angles to our line of sight, whose radiation is initially beamed away from us but its beaming cone gradually reaches our line of sight as it decelerates. One cannot distinguish between these explanations (or combinations of them) using only the X-ray to radio $F_\nu(t)$. Here we demonstrate that the most promising way to break this degeneracy is through afterglow imaging and polarization, by calculating the predicted evolution of the afterglow image (its size, shape and flux centroid) and linear polarization $\Pi(t)$ for different angular and/or radial outflow structures that fit $F_\nu(t)$. We consider two angular profiles -- a Gaussian and a narrow core with power-law wings in energy per solid angle, as well as a (cocoon motivated) (quasi-) spherical flow with radial velocity profile. For a jet viewed off-axis (and a magnetic field produced in the afterglow shock) $\Pi(t)$ peaks when the jet's core becomes visible, at $\approx2t_p$ where the lightcurve peaks at $t_p$, and the image can be elongated with aspect ratios$\;\gtrsim2$. A quasi-spherical flow has an almost circular image and a much lower $\Pi(t)$ (peaking at $\approx t_p$) and flux centroid displacement.

[4] arXiv:1803.05864v1 [pdf, vox]

The limited role of recombination energy in common envelope removal

Aldana Grichener, Efrat Sabach, Noam Soker
Submitted Thursday 15 March 2018 @ 16:59:42 GMT
To be submitted in 2 days to allow comments by readers

We calculate the outward energy transport time by convection and photon diffusion in an inflated common envelope and find this time to be shorter than the envelope expansion time. We conclude therefore that most of the hydrogen recombination energy ends in radiation rather than in kinetic energy of the outflowing envelope. We use the stellar evolution code MESA and inject energy inside the envelope of an asymptotic giant branch star to mimic energy deposition by a spiraling-in stellar companion. During 1.7 years the envelope expands by a factor of more than 2. Along the entire evolution the convection can carry the energy very efficiently outwards, to the radius where radiative transfer becomes more efficient. The total energy transport time stays within several months, shorter than the dynamical time of the envelope. Had we included rapid mass loss, as is expected in the common envelope evolution, the energy transport time would have been even shorter. It seems that calculations that assume that most of the recombination energy ends in the outflowing gas are inaccurate.

[5] arXiv:1803.05856v1 [pdf, vox]

Off-axis afterglow light curves and images from 2D hydrodynamic simulations of double-sided GRB jets in a stratified external medium

Jonathan Granot, Fabio De Colle, Enrico Ramirez-Ruiz
Submitted Thursday 15 March 2018 @ 16:48:51 GMT
8 pages, 6 figures; submitted to MNRAS

Gamma-ray burst (GRB) jets are narrow, and thus typically point away from us. They are initially ultra-relativistic, causing their prompt $\gamma$-ray and early afterglow emission to be beamed away from us. However, as the jet gradually decelerates its beaming cone widens and eventually reaches our line of sight and the afterglow emission may be detected. Such orphan afterglows were not clearly detected so far. Nevertheless, they should be detected in upcoming optical or radio surveys, and it would be challenging to clearly distinguish between them and other types of transients. Therefore, we perform detailed, realistic calculations of the expected afterglow emission from GRB jets viewed at different angles from the jet's symmetry axis. The dynamics are calculated using 2D relativistic hydrodynamics simulations of jets propagating into different power-law external density profiles, $\rho_{\rm ext}\propto{}R^{-k}$ for $k=0,\,1,\,1.5,\,2$, ranging from a uniform ISM-like medium ($k=0$) to a stratified steady stellar-wind like profile ($k=2$). We calculate radio, optical and X-ray lightcurves, and the evolution of the radio afterglow image size, shape and flux centroid. This may help identify misaligned relativistic jets, whether initially ultra-relativistic and producing a GRB for observers within their beam, or (possibly intrinsically more common) moderately relativistic, in either (i) nearby supernovae Ib/c (some of which are associated with long duration GRBs), or (ii) in binary neutron star mergers, which may produce short duration GRBs, and may also be detected in gravitational waves (e.g. GW$\,$170827/GRB$\,$​170817A with a weak prompt $\gamma$-ray emission may harbor an off-axis jet).

[6] arXiv:1803.05842v1 [pdf, vox]

Data as a Research Infrastructure - CDS, the Virtual Observatory, Astronomy, and beyond

Francoise Genova
Submitted Thursday 15 March 2018 @ 16:36:38 GMT
To be published in Proceedings of the Libraries and Information Systems in Astronomy 2018 - LISA VIII conference, held in Strasbourg, France, June 6-9,2017

The situation of data sharing in astronomy is positioned in the current general context of a political push towards, and rapid development of, scientific data sharing. Data is already one of the major infrastructures of astronomy, thanks to the data and service providers and to the International Virtual Observatory Alliance (IVOA). Other disciplines are moving on in the same direction. International organisations, in particular the Research Data Alliance (RDA), are developing building blocks and bridges to enable scientific data sharing across borders. The liaisons between RDA and astronomy, and RDA activities relevant to the librarian community, are discussed.

[7] arXiv:1803.05834v1 [pdf, vox]

On-orbit Operations and Offline Data Processing of CALET onboard the ISS

Y. Asaoka, S. Ozawa, S. Torii, O. Adriani, Y. Akaike, K. Asano, M. G. Bagliesi, G. Bigongiari, W. R. Binns, S. Bonechi, M. Bongi, P. Brogi, J. H. Buckley, N. Cannady, G. Castellini, C. Checchia, M. L. Cherry, G. Collazuol, V. Di Felice, K. Ebisawa, H. Fuke, T. G. Guzik, T. Hams, M. Hareyama, N. Hasebe, K. Hibino, M. Ichimura, K. Ioka, W. Ishizaki, M. H. Israel, A. Javaid, K. Kasahara, J. Kataoka, R. Kataoka, Y. Katayose, C. Kato, N. Kawanaka, Y. Kawakubo, K. Kohri, H. S. Krawczynski, J. F. Krizmanic, S. Kuramata, T. Lomtadze, P. Maestro, P. S. Marrocchesi, A. M. Messineo, J. W. Mitchell, S. Miyake, K. Mizutani, A. A. Moiseev, K. Mori, M. Mori, N. Mori, H. M. Motz, K. Munakata, H. Murakami, S. Nakahira, J. Nishimura, G. A. de Nolfo, S. Okuno, J. F. Ormes, L. Pacini, F. Palma, P. Papini, A. V. Penacchioni, B. F. Rauch, S. B. Ricciarini, K. Sakai, T. Sakamoto, M. Sasaki, Y. Shimizu, A. Shiomi, R. Sparvoli, P. Spillantini, F. Stolzi, I. Takahashi, M. Takayanagi, M. Takita, T. Tamura, N. Tateyama, T. Terasawa, H. Tomida, Y. Tsunesada, Y. Uchihori, S. Ueno, E. Vannuccini, J. P. Wefel, K. Yamaoka, S. Yanagita, A. Yoshida, K. Yoshida, T. Yuda
Submitted Thursday 15 March 2018 @ 16:14:19 GMT
11 pages, 7 figures, published online 27 February 2018

The CALorimetric Electron Telescope (CALET), launched for installation on the International Space Station (ISS) in August, 2015, has been accumulating scientific data since October, 2015. CALET is intended to perform long-duration observations of high-energy cosmic rays onboard the ISS. CALET directly measures the cosmic-ray electron spectrum in the energy range of 1 GeV to 20 TeV with a 2% energy resolution above 30 GeV. In addition, the instrument can measure the spectrum of gamma rays well into the TeV range, and the spectra of protons and nuclei up to a PeV. In order to operate the CALET onboard ISS, JAXA Ground Support Equipment (JAXA-GSE) and the Waseda CALET Operations Center (WCOC) have been established. Scientific operations using CALET are planned at WCOC, taking into account orbital variations of geomagnetic rigidity cutoff. Scheduled command sequences are used to control the CALET observation modes on orbit. Calibration data acquisition by, for example, recording pedestal and penetrating particle events, a low-energy electron trigger mode operating at high geomagnetic latitude, a low-energy gamma-ray trigger mode operating at low geomagnetic latitude, and an ultra heavy trigger mode, are scheduled around the ISS orbit while maintaining maximum exposure to high-energy electrons and other high-energy shower events by always having the high-energy trigger mode active. The WCOC also prepares and distributes CALET flight data to collaborators in Italy and the United States. As of August 31, 2017, the total observation time is 689 days with a live time fraction of the total time of approximately 84%. Nearly 450 million events are collected with a high-energy (E>10 GeV) trigger. By combining all operation modes with the excellent-quality on-orbit data collected thus far, it is expected that a five-year observation period will provide a wealth of new and interesting results.

[8] arXiv:1803.05810v1 [pdf, vox]

Low temperature optical properties of interstellar and circumstellar icy silicate grain analogues in the mid-infrared spectral region

Alexey Potapov, Harald Mutschke, Phillip Seeber, Thomas Henning, Cornelia Jäger
Submitted Thursday 15 March 2018 @ 15:33:22 GMT
submitted to ApJ

Two different silicate/water ice mixtures representing laboratory analogues of interstellar and circumstellar icy grains were produced in the laboratory. For the first time, optical constants, the real and imaginary parts of the complex refractive index, of such silicate/water ice mixtures were experimentally determined in the mid-infrared spectral region at low temperatures. In addition, optical constants of pure water ice and pure silicates were derived in the laboratory. Two sets of constants were compared, namely, measured constants calculated from the transmission spectra of silicate/water ice samples and effective constants calculated from the optical constants of pure silicates and pure water ice samples using different mixing rules (effective medium approaches). Differences between measured and effective constants show that a mixing (averaging) of optical constants of water ice and silicates for the determination of the optical properties of silicate/ice mixtures can lead to incorrect results. Also, it is shown that a part of water ice molecules is trapped in/on silicate grains and does not desorb up to 200 K. Our unique data are just in time with respect to the new challenging space mission, James Webb Space Telescope, which will be able to bring novel detailed information on interstellar and circumstellar grains, and suitable laboratory data are extremely important for the decoding of astronomical spectra.

[9] arXiv:1803.05803v1 [pdf, vox]

The contributions of dark matter annihilation to the global 21cm spectrum observed by the EDGES experiment

Yupeng Yang, Xiaoyuan Huang, Lei Feng
Submitted Thursday 15 March 2018 @ 15:24:08 GMT
5 pages, 1 figure. comments welcome

The EDGES experiment has observed an absorption feature in the global 21 cm spectrum with a surprisingly large amplitude. These results can be explained by decreasing the kinetic temperature of baryons, which can be achieved through the scattering between the baryons and dark matter particles. It seems that the dark matter annihilation can not explain the observed large amplitude. The main reason is that the interactions between the particles produced by the dark matter annihilation and the particles which have been present in the universe will increase the baryonic temperature. Recently, C. Feng and G. Holder have found that increasing the temperature of cosmic radio background can produce the large amplitude in the global 21 cm spectrum. In this paper, we propose that the dark matter annihilation can also produce the large amplitude observed by EDGES experiment. The main point is that although the dark matter annihilation can increase the kinetic temperature of baryons, the electrons and positrons from the dark matter annihilation can produce the synchrotron radiation in the magnetic field of the universe. These radiation will contribute and enhance the temperature of the cosmic radio background. As a result, the global 21 cm spectrum with a large absorption amplitude can be produced by the dark matter annihilation.

[10] arXiv:1803.05764v1 [pdf, vox]

Optical validation and characterization of Planck PSZ1 sources at the Canary Islands observatories. I. First year of ITP13 observations

R. Barrena, A. Streblyanska, A. Ferragamo, J. A. Rubino-Martin, A. Aguado-Barahona, D. Tramonte, R. T. Genova-Santos, A. Hempel, H. Lietzen, N. Aghanim, M. Arnaud, H. Bohringer, G. Chon, J. Democles, H. Dahle, M. Douspis, A. N. Lasenby, P. Mazzotta, J. B. Melin, E. Pointecouteau, G. W. Pratt, M. Rossetti, R. F. J. van der Burg
Submitted Thursday 15 March 2018 @ 14:14:16 GMT
To be published in A&A (already revised by the referee). 17 pages, 12 figures, 3 tables

We identify new clusters and characterize previously unknown Planck Sunyaev-Zeldovich (SZ) sources from the first Planck catalogue of SZ sources (PSZ1). The results presented here correspond to an optical follow-up observational programme developed during approximately one year (2014) at Roque de los Muchachos Observatory, using the 2.5m Isaac Newton telescope, the 3.5m Telescopio Nazionale Galileo, the 4.2m William Herschel telescope and the 10.4m Gran Telescopio Canarias. We characterize 115 new PSZ1 sources using deep optical imaging and spectroscopy. We adopt robust criteria in order to consolidate the SZ counterparts by analysing the optical richness, the 2D galaxy distribution, and velocity dispersions of clusters. Confirmed counterparts are considered to be validated if they are rich structures, well aligned with the Planck PSZ1 coordinate and show relatively high velocity dispersion. Following this classification, we confirm 53 clusters, which means that 46% of this PSZ1 subsample has been validated and characterized with this technique. Sixty-two SZ sources (54% of this PSZ1 subset) remain unconfirmed. In addition, we find that the fraction of unconfirmed clusters close to the galactic plane (at |b|<25deg) is greater than that at higher galactic latitudes (|b|>25deg), which indicates contamination produced by radio emission of galactic dust and gas clouds on these SZ detections. In fact, in the majority of the cases, we detect important galactic cirrus in the optical images, mainly in the SZ target located at low galactic latitudes, which supports this hypothesis.

[11] arXiv:1803.05739v1 [pdf, vox]

Spectroscopic and photometric observations of Symbiotic Nova PU Vul during 2009-2016

A. A. Tatarnikova, M. A. Burlak, E. A. Kolotilov, N. V. Metlova, V. I. Shenavrin, S. Yu. Shugarov, T. N. Tarasova, A. M. Tatarnikov
Submitted Thursday 15 March 2018 @ 13:30:04 GMT

A new set of low-resolution spectral and UBVJHKL-photometric observations of the symbiotic nova PU Vul is presented. The binary has been still evolving after the symbiotic nova outburst in 1977 and now it's in the nebular stage. It is found that the third orbital cycle (after 1977) was characterized by great changes in light curves. Now PU Vul demonstrates a sine-wave shape of all light curves (with an amplitude in the U band of about 0.7 mag), which is typical for symbiotic stars in quiescent state. Brightness variability due to cool component pulsations is now clearly visible in the VRI light curves. The amplitude of the pulsations increases from 0.5 mag in V band to 0.8 mag in I band. These two types of variability, as well as a very slow change of the hot component physical parameters due to evolution after the outburst of 1979, influence the spectral energy distribution of the system. The emission lines variability is highly complex. Only hydrogen lines fluxes vary with orbital phase. An important feature of the third orbital cycle is the first appearance of the OVI, 6828A Raman scattering line. We determined the hot component temperature by means of Zanstra method applied to the He II, 4686 line. Our estimate is about 150000 K for the spectrum obtained near orbital maximum in 2014. The VO spectral index derived near pulsation minimum corresponds to M6 spectral class for the cool component of PU Vul.

[12] arXiv:1803.05731v1 [pdf, vox]

The Effects of Subsurface Chemistry in the Grain Mantles on the Deuterium Chemistry in Molecular Clouds

Juris Kalvans, Ivar Shmeld
Submitted Thursday 15 March 2018 @ 13:21:53 GMT
Unpublished paper for Poster No. II.48 in IAUS 280 "The Molecular Universe" (2011). 6 pages, 2 figures

The deuterium enrichment in molecules in dark molecular cloud cores and starforming regions is usually attributed to gas-phase chemistry. Here we examine the effects of surface and mantle chemical reactions on the deuteration of species. We use a simple kinetic chemistry model that includes gas, surface and mantle pore phase reactions of deuterated species. The mantle is assumed to be partially reactive due to pores with sufficient surface area for chemical reactions, that are continuously transformed by cosmic-rays. Calculation results show that surface reactions generally enhance the deuteration for at least several molecules. However, once they are buried and become mantle molecules, they lose their deuteration over a timescale of 10 million years due to processes in the mantle. If deuterated species in young star-forming regions come from grain mantles, a cautious conclusion is that the freeze-out of molecules, perhaps, should not occur more than 10 Myr before the mantle evaporates to the gas phase.

[13] arXiv:1803.05716v1 [pdf, vox]

Magnetars: a short review and some sparse considerations

P. Esposito, N. Rea, G. L. Israel
Submitted Thursday 15 March 2018 @ 12:53:53 GMT
Review to appear in T. Belloni, M. Mendez, C. Zhang, editors, "Timing Neutron Stars: Pulsations, Oscillations and Explosions", ASSL, Springer. arXiv admin note: text overlap with arXiv:1409.2004 by other authors

We currently know about 30 magnetars: seemingly isolated neutron stars whose properties can be (in part) comprehended only acknowledging that they are endowed with magnetic fields of complex morphology and exceptional intensity-at least in some components of the field structure. Although magnetars represent only a small percentage of the known isolated neutron stars, there are almost certainly many more of them, since most magnetars were discovered in transitory phases called outbursts, during which they are particularly noticeable. In outburst, in fact, a magnetar can be brighter in X-rays by orders of magnitude and usually emit powerful bursts of hard-X/soft-gamma-ra​y photons that can be detected almost everywhere in the Galaxy with all-sky monitors such as those on board the Fermi satellite or the Neil Gehrels Swift Observatory. Magnetars command great attention because the large progress that has been made in their understanding is proving fundamental to fathom the whole population of isolated neutron stars, and because, due to their extreme properties, they are relevant for a vast range of different astrophysical topics, from the study of gamma-ray bursts and superluminous supernovae, to ultraluminous X-ray sources, fast radio bursts, and even to sources of gravitational waves. Several excellent reviews with different focuses were published on magnetars in the last few years: among others, Israel and Dall'Osso (2011); Rea and Esposito (2011); Turolla and Esposito (2013); Mereghetti et al. (2015); Turolla et al. (2015); Kaspi and Beloborodov (2017). Here, we quickly recall the history of these sources and travel through the main observational facts, trying to touch some recent and sometimes little-discussed ramifications of magnetars.

[14] arXiv:1803.05707v1 [pdf, vox]

Efficient Calibration of Radio Interferometers Using Block LDU Decomposition

Ahmad Mouri Sardarabadi, Alle-Jan van der Veen, Léon V. E. Koopmans
Submitted Thursday 15 March 2018 @ 12:21:32 GMT
EUSIPCO 2018 conference

Having an accurate calibration method is crucial for any scientific research done by a radio telescope. The next generation radio telescopes such as the Square Kilometre Array (SKA) will have a large number of receivers which will produce exabytes of data per day. In this paper we propose new direction-dependent and independent calibration algorithms that, while requiring much less storage during calibration, converge very fast. The calibration problem can be formulated as a non-linear least square optimization problem. We show that combining a block-LDU decomposition with Gauss-Newton iterations produces systems of equations with convergent matrices. This allows significant reduction in complexity per iteration and very fast converging algorithms. We also discuss extensions to direction-dependent calibration. The proposed algorithms are evaluated using simulations.

[15] arXiv:1803.05701v1 [pdf, vox]

The $^{7}$Be(n,p)$^{7}$L​i reaction and the Cosmological Lithium Problem: measurement of the cross section in a wide energy range at n_TOF (CERN)

L. Damone, M. Barbagallo, M. Mastromarco, A. Mengoni, L. Cosentino, E. Maugeri, S. Heinitz, D. Schumann, R. Dressler, F. Käppeler, N. Colonna, P. Finocchiaro, J. Andrzejewski, J. Perkowski, A. Gawlik, O. Aberle, S. Altstadt, M. Ayranov, L. Audouin, M. Bacak, J. Balibrea-Correa, J. Ballof, V. Bécares, F. Bečvář, C. Beinrucker, G. Bellia, A. P. Bernardes, E. Berthoumieux, J. Billowes, M. J. G. Borge, D. Bosnar, A. Brown, M. Brugger, M. Busso, M. Caamaño, F. Calviño, M. Calviani, D. Cano-Ott, R. Cardella, A. Casanovas, D. M. Castelluccio, R. Catherall, F. Cerutti, Y. H. Chen, E. Chiaveri, G. Cortés, M. A. Cortés-Giraldo, S. Cristallo, M. Diakaki, M. Dietz, C. Domingo-Pardo, A. Dorsival, E. Dupont, I. Duran, B. Fernandez-Dominguez, A. Ferrari, P. Ferreira, W. Furman, S. Ganesan, A. García-Rio, S. Gilardoni, T. Glodariu, K. Göbel, I. F. Gonçalves, E. González-Romero, T. D. Goodacre, E. Griesmayer, C. Guerrero, F. Gunsing, H. Harada, T. Heftrich, J. Heyse, D. G. Jenkins, E. Jericha, K. Johnston, Y. Kadi, A. Kalamara, T. Katabuchi, P. Kavrigin, A. Kimura, N. Kivel, U. Kohester, M. Kokkoris, M. Krtička, D. Kurtulgil, E. Leal-Cidoncha, C. Lederer-Woods, H. Leeb, J. Lerendegui-Marco, S. Lo Meo, S. J. Lonsdale, R. Losito, D. Macina, J. Marganiec, B. Marsh, T. Martíne, J. G. Martins Correia, A. Masi, C. Massimi, P. Mastinu, F. Matteucci, A. Mazzone, E. Mendoza, P. M. Milazzo, F. Mingrone, M. Mirea, A. Musumarra, A. Negret, R. Nolte, A. Oprea, N. Patronis, A. Pavlik, L. Piersanti, M. Piscopo, A. Plompen, I. Porras, J. Praena, J. M. Quesada, D. Radeck, K. Rajeev, T. Rauscher, R. Reifarth, A. Riego-Perez, S. Rothe, P. Rout, C. Rubbia, J. Ryan, M. Sabaté-Gilarte, A. Saxena, J. Schell, P. Schillebeeckx, S. Schmidt, P. Sedyshev, C. Seiffert, A. G. Smith, N. V. Sosnin, A. Stamatopoulos, T. Stora, G. Tagliente, J. L. Tain, A. Tarifeño-Saldivia, L. Tassan-Got, A. Tsinganis, S. Valenta, G. Vannini, V. Variale, P. Vaz, A. Ventura, V. Vlachoudis, R. Vlastou, A. Wallner, S. Warren, M. Weigand, C. Weiß, C. Wolf, P. J. Woods, T. Wright, P. Žugec
Submitted Thursday 15 March 2018 @ 11:51:17 GMT

We report on the measurement of the $^{7}$Be($n, p$)$^{7}$Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the Big Bang Nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and showed a large discrepancy between each other. The measurement was performed with a Si-telescope, and a high-purity sample produced by implantation of a $^{7}$Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low-energy, relative to current evaluations, in the region of BBN interest the present results are consistent with the values inferred from the time-reversal $^{7}$Li($p, n$)$^{7}$Be reaction, thus yielding only a relatively minor improvement on the so-called Cosmological Lithium Problem (CLiP). The relevance of these results on the near-threshold neutron production in the p+$^{7}$Li reaction is also discussed.

[16] arXiv:1803.05699v1 [pdf, vox]

Probing the energy spectrum of hadrons produced in cosmic-ray interactions at ultrahigh energies through the fluctuations of the muon content of extensive air showers

Lorenzo Cazon, Ruben Conceição, Felix Riehn
Submitted Thursday 15 March 2018 @ 11:38:06 GMT

We demonstrate that the shower-to-shower fluctuations of the muon content of extensive air showers correlate with the fluctuations of a variable of the first interaction of Ultra High Energy Cosmic Rays, which is computed from the fraction of energy carried by the hadrons that sustain the hadronic cascade. The influence of subsequent stages of the shower development is found to play a sub-dominant role. As a consequence, the shower-to-shower distribution of the muon content is a direct probe of the hadron energy spectrum of interactions beyond 100 TeV center of mass energies.

[17] arXiv:1803.05697v1 [pdf, vox]

FRB microstructure revealed by the real-time detection of FRB170827

W. Farah, C. Flynn, M. Bailes, A. Jameson, K. W. Bannister, E. D. Barr, T. Bateman, S. Bhandari, M. Caleb, D. Campbell-Wilson, S. -W. Chang, A. Deller, A. J. Green, R. Hunstead, F. Jankowski, E. Keane, J. -P. Macquart, A. Möller, C. A. Onken, S. Osłowski, A. Parthasarathy, V. Ravi, R. Shannon, B. E. Tucker, V. Venkatraman Krishnan, C. Wolf
Submitted Thursday 15 March 2018 @ 11:24:27 GMT
10 pages, 6 figures, submitted to MNRAS

We report a new Fast Radio Burst (FRB) discovered in real-time as part of the UTMOST project at the Molonglo Observatory Synthesis Radio Telescope (MOST). FRB170827 is the first detected with our low-latency ($< 24$ s), machine-learning-bas​ed FRB detection system. The FRB discovery was accompanied by the capture of voltage data at the native time and frequency resolution of the observing system, enabling coherent dedispersion and detailed off-line analysis, which have unveiled fine temporal and frequency structure. The dispersion measure (DM) of 176.80 $\pm$ 0.04 pc cm$^{-3}$, is the lowest of the FRB population. The Milky Way contribution along the line of sight is $\sim$ 40 pc cm$^{-3}$, leaving an excess DM of $\sim$ 145 pc cm$^{-3}$. The FRB has a fluence $>$ 20 $\pm$ 7 Jy ms. The burst's width at 10$\%$ maximum is 400 $\mu$s, making it one of the narrowest FRBs. The burst shows three temporal components, the narrowest of which is $\sim$ 30 $\mu$s, and a scattering of $4.1 \pm 2.7$ $\mu$s. The FRB shows spectral modulations on frequency scales of 1.5 MHz and 0.1 MHz. Both are prominent in the dynamic spectrum, which shows a bright region of emission between 841 and 843 MHz, and weaker, patchy emission across the entire band. We show the fine spectral structure could arise in the FRB host galaxy, or its immediate vicinity.

[18] arXiv:1803.05686v1 [pdf, vox]

Cosmic-rays, gas, and dust in nearby anti-centre clouds : III -- Dust extinction, emission, and grain properties

Q. Remy, I. A. Grenier, D. J. Marshall, J. M. Casandjian
Submitted Thursday 15 March 2018 @ 10:53:33 GMT

We have explored the capabilities of dust extinction and $\gamma$ rays to probe the properties of the interstellar medium in the nearby anti-centre region. We have jointly modelled the $\gamma$-ray intensity and the stellar reddening, E(B-V) as a combination of H$_{\rm I}$-bright, CO-bright, and ionised gas components. The complementary information from dust reddening and $\gamma$ rays is used to reveal the dark gas not seen, or poorly traced, by H$_{\rm I}$, free-free, and $^{12}$CO emissions. We compare the total gas column densities, $N_{\rm{H}}$, derived from the $\gamma$ rays and stellar reddening with those inferred from a similar analysis (Remy et al. 2017) of $\gamma$ rays and of the optical depth of the thermal dust emission, $\tau_{353}$, at 353 GHz. We can therefore compare environmental variations in specific dust reddening, E(B-V)/$N_{\rm H}$, and in dust emission opacity (dust optical depth per gas nucleon), $\tau_{353}/N_{\rm{H​}}$. Over the whole anti-centre region, we find an average E(B-V)/$N_{\rm H}$ ratio of $(2.02\pm0.48)\times​$ $10^{-22}$~mag~cm$^2​$, with maximum local variations of about $\pm30\%$ at variance with the two to six fold coincident increase seen in emission opacity as the gas column density increases. In the diffuse medium, the small variations in specific reddening, E(B-V)/$N_{\rm H}$ implies a rather uniform dust-to-gas mass ratio in the diffuse parts of the anti-centre clouds. The small amplitude of the E(B-V)/$N_{\rm H}$ variations with increasing $N_{\rm{H}}$ column density confirms that the large opacity $\tau_{353}/N_{\rm{H​}}$ rise seen toward dense CO clouds is primarily due to changes in dust emissivity. The environmental changes are qualitatively compatible with model predictions based on mantle accretion on the grains and the formation of grain aggregates.

[19] arXiv:1803.05677v1 [pdf, vox]

GJ1214: Rotation period, starspots, and uncertainty on the optical slope of the transmission spectrum

M. Mallonn, E. Herrero, I. G. Juvan, C. von Essen, A. Rosich, I. Ribas, T. Granzer, X. Alexoudi, K. G. Strassmeier
Submitted Thursday 15 March 2018 @ 10:28:26 GMT
11 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

Brightness inhomogeneities in the stellar photosphere (dark spots or bright regions) affect the measurements of the planetary transmission spectrum. To investigate the star spots of the M dwarf GJ 1214, we conducted a multicolor photometric monitoring from 2012 to 2016. The measured variability shows a periodicity of 125 +- 5 days, which we interpret as the signature of the stellar rotation period. This value overrules previous suggestions of a significantly shorter stellar rotation period. A light curve inversion of the monitoring data yields an estimation of the flux dimming of a permanent spot filling factor not contributing to the photometric variability, a temperature contrast of the spots of about 370 K and persistent active longitudes. The derived surface maps over all five seasons were used to estimate the influence of the star spots on the transmission spectrum of the planet from 400 nm to 2000 nm. The monitoring data presented here do not support a recent interpretation of a measured transmission spectrum of GJ 1214b as to be caused by bright regions in the stellar photosphere. Instead, we list arguments as to why the effect of dark spots likely dominated over bright regions in the period of our monitoring. Furthermore, our photometry proves an increase in variability over at least four years, indicative for a cyclic activity behavior. The age of GJ 1214 is likely between 6 and 10 Gyr. The long-term photometry allows for a correction of unocculted spots. For an active star such as GJ 1214, there remains a degeneracy between occulted spots and the transit parameters used to build the transmission spectrum. This degeneracy can only be broken by high-precision transit photometry resolving the spot crossing signature in the transit light curve.

[20] arXiv:1803.05650v1 [pdf, vox]

Decaying warm dark matter and structure formation

Jui-Lin Kuo, Massimiliano Lattanzi, Kingman Cheung, José W. F. Valle
Submitted Thursday 15 March 2018 @ 09:20:22 GMT
21 pages, 6 figure

We examine the cosmology of warm dark matter (WDM), both stable and decaying, from the point of view of structure formation. We compare the matter power spectrum associated to WDM masses of 1.5 keV and 0.158 keV, with that expected for the stable cold dark matter $\Lambda$CDM paradigm, taken as our reference model. We scrutinize the effects associated to the warm nature of dark matter, as well as the fact that it decays. The decaying warm dark matter (DWDM) scenario is well-motivated, emerging in a broad class of particle physics theories where neutrino masses arises from the spontaneous breaking of a continuous global lepton number symmetry. The majoron arises as a Nambu-Goldstone boson, and picks up a mass from gravitational effects, that explicitly violate global symmetries. The majoron necessarily decays to neutrinos, with an amplitude proportional to their tiny mass, which typically gives it cosmologically long lifetimes. Using state-of-the-art N-body simulations we show that our DWDM picture leads to a viable alternative to the $\Lambda$CDM scenario, with predictions that can differ substantially on small scales.

[21] arXiv:1803.05638v1 [pdf, vox]

$f(R)$ gravity modifications: from the action to the data

Ruth Lazkoz, María Ortiz-Baños, Vincenzo Salzano
Submitted Thursday 15 March 2018 @ 08:48:26 GMT
12 pages;

It is a very well established matter nowadays that many modified gravity models can offer a sound alternative to General Relativity for the description of the accelerated expansion of the universe. But it is also equally well known that no clear and sharp discrimination between any alternative theory and the classical one has been found so far. In this work, we attempt at formulating a different approach starting from the general class of $f(R)$ theories as test probes: we try to reformulate $f(R)$ Lagrangian terms as explicit functions of the redshift, i.e., as $f(z)$. In this context, the $f(R)$ setting to the consensus cosmological model, the $\Lambda$CDM model, can be written as a polynomial including just a constant and a third-order term. Starting from this result, we propose various different polynomial parameterizations $f(z)$, including new terms which would allow for deviations from $\Lambda$CDM, and we thoroughly compare them with observational data. While on the one hand we have found no statistically preference for our proposals (even if some of them are as good as $\Lambda$CDM by using Bayesian Evidence comparison), we think that our novel approach could provide a different perspective for the development of new and observationally reliable alternative models of gravity.

[22] arXiv:1803.05623v1 [pdf, vox]

Long-Term Cyclicities in Phanerozoic Sea-Level Sedimentary Record and their Potential Drivers

Slah Boulila, Jacques Laskar, Bilal U. Haq, Bruno Galbrun, Nathan Hara
Submitted Thursday 15 March 2018 @ 08:04:26 GMT
47 pages, 19 figures, Accepted for publication in Global and Planetary Change

Cyclic sedimentation has varied at several timescales and this variability has been geologically well documented at Milankovitch timescales, controlled in part by climatically (insolation) driven sea-level changes. At the longer (tens of Myr) timescales connection between astronomical parameters and sedimentation via cyclic solar-system motions within the Milky Way has also been proposed, but this hypothesis remains controversial because of the lack of long geological records. The absence of a physical mechanism that could explain the connection between climate and astronomy at these longer timescales led to the explanation of plate motions as the main driver of climate on Earth. Here we statistically show a prominent and persistent ~36 Myr sedimentary cyclicity superimposed on two megacycles (~250 Myr) in a relatively well-constrained sea-level (SL) record of the past 542 Myr (Phanerozoic eon). Given the possible link between amplitudes of the ~36 and ~250 Myr cyclicities in SL record and the potential that these periodicities fall into the frequency band of solar system motions, we suggest an astronomical origin, and model these periodicities as originating from the path of the solar system in the Milky Way as vertical and radial periods that modulate the flux of cosmic rays on Earth. Our finding of the ~36 Myr SL cyclicity lends credibility to the existing hypothesis about the imprint of solar-system vertical period on the geological record. The ~250 Myr megacycles are tentatively attributed to a radial period. However, the tectonic drivers also remain potentially plausible. The potential existence of a correlation between the modeled astronomical signal and the geological record may offer an indirect proxy to understand the structure and history of the Milky Way by providing a 542 Myr long record of the path of the Sun in our Galaxy.

[23] arXiv:1803.05556v1 [pdf, vox]

Electron and Proton Acceleration in Trans-Relativistic Magnetic Reconnection: Dependence on Plasma Beta and Magnetization

David Ball, Lorenzo Sironi, Feryal Özel
Submitted Thursday 15 March 2018 @ 00:59:23 GMT
19 pages, 23 figures, submitted to ApJ

Non-thermal electron acceleration via magnetic reconnection is thought to play an important role in powering the variable X-ray emission from radiatively inefficient accretion flows around black holes. The trans-relativistic regime of magnetic reconnection, where the magnetization $\sigma$, defined as the ratio of magnetic energy density to enthalpy density, is $\sim 1$, is frequently encountered in such flows. By means of a large suite of two-dimensional particle-in-cell simulations, we investigate electron and proton acceleration in the trans-relativistic regime. We focus on the dependence of the electron energy spectrum on $\sigma$ and the proton $\beta$ (i.e., the ratio of proton thermal pressure to magnetic pressure). We find that the electron spectrum in the reconnection region is non-thermal and can be generally modeled as a power law. At $\beta \lesssim 3 \times 10^{-3}$, the slope, $p$, is independent of $\beta$ and it hardens with increasing $\sigma$ as $p\simeq 1.8 +0.7/\sqrt{\sigma}$. Electrons are primarily accelerated by the non-ideal electric field at X-points, either in the initial current layer or in current sheets generated in between merging magnetic islands. At higher values of $\beta$, the electron power law steepens for all values of $\sigma$. At values of $\beta$ near $\beta_{\rm max}\approx1/4\sigma​$, when both electrons and protons are relativistically hot prior to reconnection, the spectra of both species display an additional component at high energies, containing a few percent of particles. These particles are accelerated via a Fermi-like process by bouncing in between the reconnection outflow and a stationary magnetic island. We provide an empirical prescription for the dependence of the power-law slope and the acceleration efficiency on $\beta$ and $\sigma$, which can be used in global simulations of collisionless accretion disks.

[24] arXiv:1803.03305v3 [pdf, vox]

The Evolution of Environmental Quenching Timescales to $z\sim1.6$

R. Foltz, G. Wilson, A. Muzzin, M. C. Cooper, J. Nantais, R. F. J. van der Burg, P. Cerulo, J. Chan, S. P. Fillingham, J. Surace, T. Webb, A. Noble, M. Lacy, M. McDonald, G. Rudnick, C. Lidman, R. Demarco, J. Hlavacek-Larrondo, H. K. C. Yee, S. Perlmutter, B. Hayden
Submitted Thursday 15 March 2018 @ 00:24:18 GMT

Using a sample of 4 galaxy clusters at $1.35 < z < 1.65$ and 10 galaxy clusters at $0.85 < z < 1.35$, we measure the environmental quenching timescale, $t_Q$, corresponding to the time required after a galaxy is accreted by a cluster for it to fully cease star formation. Cluster members are selected by a photometric-redshift criterion, and categorized as star-forming, quiescent, or intermediate according to their dust-corrected rest-frame colors and magnitudes. We employ a "delayed-then-rapid" quenching model that relates a simulated cluster mass accretion rate to the observed numbers of each type of galaxy in the cluster to constrain $t_Q$. For galaxies of mass $M_* \gtrsim 10^{10.5}~ \mathrm{M}_\odot$, we find a quenching timescale of $t_Q=$ 1.24 Gyr in the $z\sim1.5$ cluster sample, and $t_Q=$ 1.50 Gyr at $z\sim1$. Using values drawn from the literature, we compare the redshift evolution of $t_Q$ to timescales predicted for different physical quenching mechanisms. We find $t_Q$ to depend on host halo mass such that quenching occurs over faster timescales in clusters relative to groups, suggesting that properties of the host halo are responsible for quenching high-mass galaxies. Between $z=0$ and $z=1.5$, we find that $t_Q$ evolves faster than the molecular gas depletion timescale and slower than an SFR-outflow timescale, but is consistent with the evolution of the dynamical time. This suggests that environmental quenching in these galaxies is driven by the motion of satellites relative to the cluster environment, although due to uncertainties in the atomic gas budget at high redshift, we cannot rule out quenching due to simple gas depletion.

Submitted Wed, 14 Mar 2018

[25] arXiv:1803.05534v1 [pdf, vox]

Las antenas de espacio profundo en la Argentina

Marcelo Colazo
Submitted Wednesday 14 March 2018 @ 23:09:37 GMT
Accepted in BAAA. in Spanish

Since December 2012, the Deep Space Antenna DS3 of the European Space Agency was inaugurated in the province of Mendoza. The possibility of using this equipment for space and scientific activities was promoted by our country. Several scientific institutions in the country are working together so that part of the observation time assigned to Argentina can be used by the astronomical community. Some results have already been presented at meetings of the AAA. Now the Deep Space antenna that China has installed in the province of Neuquen as part of its Lunar Exploration Program is added to the Argentine observational capabilities. This paper describes the characteristics of the new station and the role that Argentina has in this project through its space agency, CONAE.

[26] arXiv:1803.05522v1 [pdf, vox]

Observational constraints on the tilted flat-XCDM and the untilted non-flat XCDM dynamical dark energy inflation parameterizations

Chan-Gyung Park, Bharat Ratra
Submitted Wednesday 14 March 2018 @ 22:01:09 GMT
20 pages, 11 figures, 8 tables. arXiv admin note: substantial text overlap with arXiv:1801.00213

We constrain tilted spatially-flat and untilted non-flat XCDM dynamical dark energy inflation parameterizations with the Planck 2015 cosmic microwave background (CMB) anisotropy data and recent Type Ia supernovae measurements, baryonic acoustic oscillations data, growth rate observations, and Hubble parameter measurements. Inclusion of the four non-CMB data sets leads to a significant strengthening of the evidence for non-flatness in the non-flat XCDM model from 1.1$\sigma$ for the CMB data alone to 3.4$\sigma$ for the full data combination. In this untilted non-flat XCDM case the data favor a spatially-closed model in which spatial curvature contributes a little less than a percent of the current cosmological energy budget; they also mildy favor dynamical dark energy over a cosmological constant at 1.2$\sigma$. These data are also better fit by the flat-XCDM parameterization than by the standard $\Lambda$CDM model, but only at 0.6$\sigma$ significance. Current data is unable to rule out dark energy dynamics. The non-flat XCDM parameterization is more consistent with the Dark Energy Survey constraints on the current value of the rms amplitude of mass fluctuations ($\sigma_8$) as a function of the current value of the nonrelativistic matter density parameter ($\Omega_m$) but does not provide as good a fit to the smaller-angle CMB anisotropy data as does the standard tilted flat-$\Lambda$CDM model. Some measured cosmological parameter values differ significantly when determined using the tilted flat-XCDM and the non-flat XCDM parameterizations, including the baryonic matter density parameter and the reionization optical depth.

[27] arXiv:1803.05508v1 [pdf, vox]

Dark matter constraints from dwarf galaxies: a data-driven analysis

Francesca Calore, Pasquale D. Serpico, Bryan Zaldivar
Submitted Wednesday 14 March 2018 @ 20:57:18 GMT

Dwarf galaxies represent a powerful probe of annihilating dark matter particle models, with gamma-ray data setting some of the best bounds available. A major issue in improving over existing constraints consists in the limited knowledge of the astrophysical background (mostly diffuse photons, but also unresolved sources). Perhaps more worrisome, several approaches in the literature suffer of the difficulty of assessing the systematic error due to background mis-modelling. Here we propose a data-driven method to estimate the background at the dwarf position and its uncertainty, relying on an appropriate use of the whole-sky data, via an optimisation procedure of the interpolation weights. While this article is mostly methodologically oriented, we also report the bounds based on latest Fermi-LAT data and updated information for J-factors for both isolated and stacked dwarfs. Our results are very competitive with the Fermi-LAT ones, while being derived with a more general and flexible method. We discuss the impact of profiling over the J-factor as well as over the background probability distribution function, with the latter resulting for instance crucial in drawing conclusions of compatibility with DM interpretations of the so-called Galactic Centre Excess.

[28] arXiv:1803.05481v1 [pdf, vox]

As a matter of force - Systematic biases in idealized turbulence simulations

Philipp Grete, Brian W. O'Shea, Kris Beckwith
Submitted Wednesday 14 March 2018 @ 19:09:24 GMT
9 page, 4 figures, under review

Many astrophysical systems encompass very large dynamical ranges in space and time, which are not accessible by direct numerical simulations. Thus, idealized subvolumes are often used to study small-scale effects including the dynamics of turbulence. These turbulent boxes require an artificial driving in order to mimic energy injection from large-scale processes. In this Letter, we show and quantify how the autocorrelation time of the driving and its normalization systematically change properties of an isothermal compressible magnetohydrodynamic flow in the sub- and supersonic regime and affect astrophysical observations such as Faraday rotation. For example, we find that $\delta$-in-time forcing with a constant energy injection leads to a steeper slope in kinetic energy spectrum and less efficient small-scale dynamo action. In general, we show that shorter autocorrelation times require more power in the acceleration field, which results in more power in compressive modes that weaken the anticorrelation between density and magnetic field strength. Thus, derived observables, such as the line-of-sight magnetic field from rotation measures, are systematically biased by the driving mechanism. We argue that $\delta$-in-time forcing is unrealistic and numerically unresolved, and conclude that special care needs to be taken in interpreting observational results based on the use of idealized simulations.

[29] arXiv:1803.05476v1 [pdf, vox]

On the universal GeV emission in binary-driven hypernovae and their inferred morphological structure

R. Ruffini, R. Moradi, Y. Wang, Y. Aimuratov, M. Amiri, L. Becerra, C. L. Bianco, Y. -C. Chen, B. Eslam Panah, G. J. Mathews, M. Muccino, G. B. Pisani, D. Primorac, J. A. Rueda
Submitted Wednesday 14 March 2018 @ 19:00:49 GMT
Submitted to ApJ

We address the significance of the observed GeV emission from \textit{Fermi}-LAT on the understanding of the structure of long GRBs. We examine 82 X-ray Flashs (XRFs), in none of them GeV radiation is observed, adding evidence to the absence of a black hole (BH) formation in their merging process. By examining $329$ Binary-driven Hypernovae (BdHNe) we find that out of $48$ BdHNe observable by \textit{Fermi}-LAT in \textit{only} $21$ of them the GeV emission is observed. The Gev emission in BdHNE follows a universal power-law relation between the luminosity and time, when measured in the rest frame of the source. The power-law index in BdHNe is of $-1.20 \pm 0.04$, very similar to the one discovered in S-GRBs, $-1.29 \pm 0.06$. The GeV emission originates from the newly-born BH and allows to determine its mass and spin. We further give the first evidence for observing a new GRB subclass originating from the merging of a hypernova (HN) and an already formed BH binary companion. We conclude that the GeV emission is a necessary and sufficient condition to confirm the presence of a BH in the hypercritical accretion process occurring in a HN. The remaining $27$ BdHNe, recently identified as sources of flaring in X-rays and soft gamma-rays, have no GeV emission. From this and previous works, we infer that the observability of the GeV emission in some BdHNe is hampered by the presence of the HN ejecta. We conclude that the GeV emission can only be detected when emitted within a half-opening angle $\approx$60$^{\circ}​$ normal to the orbital plane of the BdHN.

[30] arXiv:1803.05459v1 [pdf, vox]

Subcritical transition to turbulence in accretion disc boundary layer

V. V. Zhuravlev, D. N. Razdoburdin
Submitted Wednesday 14 March 2018 @ 18:12:40 GMT
submitted to A&A

Enhanced angular momentum transfer through the boundary layer near the surface of weakly magnetised accreting star is required in order to explain the observed accretion timescales in low-mass X-ray binaries, cataclysmic variables or young stars with massive protoplanetary discs. Accretion disc boundary layer is locally represented by incompressible homogeneous and boundless flow of the cyclonic type, which is linearly stable. Its non-linear instability at the shear rates of order of the rotational frequency remains an issue. We argue that hydrodynamical subcritical turbulence in such a flow is sustained by the non-linear feedback from essentially three-dimensional vortices, which are generated by quasi-two-dimensiona​l trailing shearing spirals grown to high amplitude via the swing amplification. We refer to those three-dimensional vortices as cross-rolls, since they are aligned in the shearwise direction in contrast to streamwise rolls generated by the anti-lift-up mechanism in rotating shear flow on the Rayleigh line. Transient growth of cross-rolls is studied analytically and further confronted with direct numerical simulations (DNS) of dynamics of non-linear erturbations. DNS performed in a tall box show that transition Reynolds number $R_T$ as function of shear rate accords with the line of constant maximum transient growth of cross-rolls. The transition in the tall box has been observed until the shear rate three times higher than the rotational frequency, when $R_T\sim 50000$. Assuming that the cross-rolls are also responsible for turbulence in the Keplerian flow, we estimate $R_T\lesssim 10^8$ in this case. The most favourable shear rate to test the existence of turbulence in the quasi-Keplerian regime may be sub-Keplerian and equal approximately to $1/2$.

[31] arXiv:1803.05455v1 [pdf, vox]

Deep JVLA Imaging of GOODS-N at 20cm

Frazer N. Owen
Submitted Wednesday 14 March 2018 @ 18:03:45 GMT
Accepted ApJSS; Paper with full resolution figures and electronic tables at http://www.aoc.nrao.​edu/~fowen/papers/GO​ODSN/

New wideband continuum observations in the 1 - 2 GHz band of the GOODS-N field using NSF's Karl G. Jansky Very Large Array (VLA) are presented. The best image with an effective frequency of 1525 MHz reaches an rms noise in the field center of 2.2 uJy with 1.6" resolution. A catalog of 795 sources is presented covering a radius of nine arcminutes centered near the nominal center for the GOODS-N field, very near the nominal VLA pointing center for the observations. Optical/NIR identifications and redshift estimates both from ground-based and HST observations are discussed. Using these optical/NIR data, it is most likely that fewer than 2 per cent of the sources without confusion problems do not have a correct identification. A large subset of the detected sources have radio sizes > 1". It is shown that the radio orientations for such sources correlate well with the HST source orientations especially for z < 1. This suggests that a least a large subset of the 10kpc-scale disks of LIRG/ULIRG galaxies have strong star-formation, not just in the nucleus. For the half of the objects with z > 1, the sample must be some mixture of very high star-formation rates, typically 300 M_sun/yr assuming pure star-formation, and an AGN or a mixed AGN/star-formation population.

[32] arXiv:1803.05453v1 [pdf, vox]

Using Ground-Based Telescopes to Mature Key Technologies and Advance Science for Future NASA Exoplanet Direct Imaging Missions

Thayne Currie, Ruslan Belikov, Olivier Guyon, N. Jeremy Kasdin, Christian Marois, Mark Marley, Kerri Cahoy, Michael McElwain, Eduardo Bendek, Marc Kuchner, Michael Meyer
Submitted Wednesday 14 March 2018 @ 18:02:14 GMT
6 pages and 2 figures; White paper submitted to the Exoplanet Science Strategy study of the National Academies of Sciences, Engineering and Medicine

Ground-based telescopes have been playing a leading role in exoplanet direct imaging science and technological development for the past two decades and will continue to have an indispensable role for the next decade and beyond. Extreme adaptive optics (AO) systems will advance focal-plane wavefront control and coronagraphy, augmenting the performance of and mitigating risk for WFIRST-CGI, while validating performance requirements and motivating improvements to atmosphere models needed to unambiguously characterize solar system-analogues with HabEx/LUVOIR. Specialized instruments for Extremely Large Telescopes may deliver the first thermal infrared images of rocky planets around Sun-like stars, providing HabEx/LUVOIR with numerous exo-Earth candidates and key ancillary information that can help clarify whether the planets are habitable.

[33] arXiv:1803.05450v1 [pdf, vox]

Probing the nature of Dark Matter through the metal enrichment of the intergalactic medium

Jonas Bremer, Pratika Dayal, Emma V. Ryan-Weber
Submitted Wednesday 14 March 2018 @ 18:01:23 GMT
Submitted to MNRAS. Comments welcome

We focus on exploring the metal enrichment of the intergalactic medium (IGM) in Cold and Warm (1.5 and 3 keV) Dark Matter (DM) cosmologies, and the constraints this yields on the DM particle mass, using a semi-analytic model, Delphi, that jointly tracks the Dark Matter and baryonic assembly of galaxies at $z \simeq 4-20$ including both Supernova and (a range of) reionization feedback (models). We find that while ${\rm M_{UV}} \geq -15$ galaxies contribute half of all IGM metals in the Cold Dark Matter model by $z \simeq 4.5$, given the suppression of low-mass halos, larger halos with ${\rm M_{UV}} \leq -15$ provide about 80\% of the IGM metal budget in 1.5 keV Warm Dark Matter models using two different models for the metallicity of the interstellar medium. Our results also show that the only models compatible with two different high-redshift data sets, provided by the evolving Ultra-Violet luminosity function at $z \simeq 6-10$ and IGM metal density (e.g. Simcoe et al. 2011), are standard Cold Dark Matter and 3 keV Warm DM that do not include any reionization feedback; a combination of the UV LF and the Diaz et al. (2016) points provides a weaker constraint, allowing Cold and 3 keV and 1.5 keV Warm DM models with SN feedback only, as well as CDM with complete gas suppression of all halos with $v_{circ} \leq 30\, {\rm km\, s^{-1}}$. Tightening the error bars on the IGM metal enrichment, future observations, at $z \geq 5.5$, could therefore represent an alternative way of shedding light on the nature of Dark Matter.

[34] arXiv:1803.05448v1 [pdf, vox]

Did ASAS-SN Kill the Supermassive Black Hole Binary Candidate PG1302-102?

Tingting Liu, Suvi Gezari, M. Coleman Miller
Submitted Wednesday 14 March 2018 @ 18:01:04 GMT
Submitted to ApJ Letters

Graham et al. (2015a) reported a periodically varying quasar and supermassive black hole binary candidate, PG1302-102 (hereafter PG1302), which was discovered in the Catalina Real-Time Transient Survey (CRTS). Its CRTS optical light curve is well fitted to a sinusoid of an observed period of $\approx 1,884$ days and well modeled by the relativistic Doppler boosting of the secondary mini-disk (D'Orazio et al. 2015). However, the CRTS light curve from MJD $\approx 53500$ to MJD $\approx 56400$ covers only ~1.5 cycles of periodic variation, a short baseline that can be highly susceptible to normal, stochastic quasar variability (Vaughan et al. 2016). In this Letter, we present a re-analysis of PG1302, using the latest light curve from the All-Sky Automated Survey for Supernovae (ASAS-SN), which extends the observational baseline to the present day (MJD $\approx 58200$), and adopting a maximum likelihood method which searches for a periodic component in addition to stochastic quasar variability. The extended ASAS-SN light curve does not support the persistence of its periodicity, and thus the suggested binary model of PG1302 is disfavored.

[35] arXiv:1803.05447v1 [pdf, vox]

The Origin of Faint Tidal Features Around Galaxies in the RESOLVE Survey

Callie E. Hood, Sheila J. Kannappan, David V. Stark, Ian P. Dell'Antonio, Amanda J. Moffett, Kathleen D. Eckert, Mark A. Norris, David Hendel
Submitted Wednesday 14 March 2018 @ 18:01:02 GMT
24 pages, 26 Figures, accepted for publication in ApJ. Full version of table 2 is available at http://resolve.astro​

We study tidal features (TFs) around galaxies in the REsolved Spectroscopy of a Local VolumE (RESOLVE) survey. Our sample consists of 1048 RESOLVE galaxies that overlap with the DECam Legacy Survey, which reaches an r-band 3$\sigma$ depth of $\sim$27.9 mag arcsec$^{-2}$ for a 100 arcsec$^{2}$ feature. Images were masked, smoothed, and inspected for TFs like streams, shells, or tails/arms. We find TFs in 17$^{\pm 2} \%$ of our galaxies, setting a lower limit on the true frequency. The frequency of TFs in the gas-poor (gas-to-stellar mass ratio $<$ 0.1) subsample is lower than in the gas-rich subsample (13$^{\pm 3} \%$ vs. 19$^{\pm 2} \%$). Within the gas-poor subsample, galaxies with TFs have higher stellar and halo masses, $\sim 3\times$ closer distances to nearest neighbors (in the same group), and possibly fewer group members at fixed halo mass than galaxies without TFs, but similar specific star formation rates. These results suggest TFs in gas-poor galaxies are typically streams/shells from dry mergers or satellite disruption. In contrast, the presence of TFs around gas-rich galaxies does not correlate with stellar or halo mass, suggesting these TFs are often tails/arms from resonant interactions. Similar to TFs in gas-poor galaxies, TFs in gas-rich galaxies imply 1.7x closer nearest neighbors in the same group; however, TFs in gas-rich galaxies are associated with diskier morphologies, higher star formation rates, and higher gas content. In addition to interactions with known neighbors, we suggest that TFs in gas-rich galaxies may arise from accretion of cosmic gas and/or gas-rich satellites below the survey limit.

[36] arXiv:1803.05446v1 [pdf, vox]

Does circumgalactic OVI trace low-pressure gas beyond the accretion shock? Clues from HI and low-ion absorption, line kinematics, and dust extinction

Jonathan Stern, Claude-André Faucher-Giguère, Joseph F. Hennawi, Zachary Hafen, Sean D. Johnson, Drummond Fielding
Submitted Wednesday 14 March 2018 @ 18:00:11 GMT
24 pages, 11 figures, resubmitted to ApJ following referee report

Large OVI columns are observed around star-forming, low-redshift ~L* galaxies, with a dependence on impact parameter indicating that most O^5+ particles reside beyond half the halo virial radius (>~100 kpc). In order to constrain the nature of the gas traced by OVI, we analyze additional observables of the outer halo, namely HI to OVI column ratios of 1-10, an absence of low-ion absorption, a mean differential extinction of E(B-V)~10^-3, and a linear relation between OVI column and velocity width. We contrast these observations with two physical scenarios: (1) OVI traces high-pressure (~30 cm^-3 K) collisionally-ionize​d gas cooling from a virially-shocked phase, and (2) OVI traces low-pressure (<~1 cm^-3 K) gas beyond the accretion shock, where the gas is in ionization and thermal equilibrium with the UV background. We demonstrate that the high-pressure scenario requires multiple gas phases to explain the observations, and a large deposition of energy at >~100 kpc to offset the energy radiated by the cooling gas. In contrast, the low-pressure scenario can explain all considered observations with a single gas phase in thermal equilibrium, provided that the baryon overdensity is comparable to the dark-matter overdensity, and that the gas is enriched to >~Z_sun/3 with an ISM-like dust-to-metal ratio. The low-pressure scenario implies that OVI traces a cool flow with mass flow rate of ~5 M_sun yr^-1, comparable to the star formation rate of the central galaxies. The OVI line widths are consistent with the velocity shear expected within this flow. The low-pressure scenario predicts a bimodality in absorption line ratios at ~100 kpc, due to the pressure jump across the accretion shock.

[37] arXiv:1803.05445v1 [pdf, vox]

Chaos and Variance in Galaxy Formation

B. W. Keller, J. W. Wadsley, L. Wang, J. M. Diederik Kruijssen
Submitted Wednesday 14 March 2018 @ 18:00:07 GMT
MNRAS submitted, comments welcome

The evolution of galaxies is governed by equations with chaotic solutions: gravity and compressible hydrodynamics. While this micro-scale chaos and stochasticity has been well studied, it is poorly understood how it couples to macro-scale properties examined in simulations of galaxy formation. In this paper, we show how perturbations introduced by floating-point roundoff, random number generators, and seemingly trivial differences in algorithmic behaviour can produce non-trivial differences in star formation histories, circumgalactic medium (CGM) properties, and the distribution of stellar mass. We examine the importance of stochasticity due to discreteness noise, variations in merger timings and how self-regulation moderates the effects of this stochasticity. We show that chaotic variations in stellar mass can grow until halted by feedback-driven self-regulation or gas exhaustion. We also find that galaxy mergers are critical points from which large (as much as a factor of 2) variations in quantities such as the galaxy stellar mass can grow. These variations can grow and persist for more than a Gyr before regressing towards the mean. These results show that detailed comparisons of simulations require serious consideration of the magnitude of effects compared to run-to-run chaotic variation, and may significantly complicate interpreting the impact of different physical models. Understanding the results of simulations requires us to understand that the process of simulation is not a mapping of an infinitesimal point in configuration space to another, final infinitesimal point. Instead, simulations map a point in a space of possible initial conditions points to a volume of possible final states.

[38] arXiv:1803.05444v1 [pdf, vox]

When do star clusters become multiple star systems? II. Toward a half-life formalism with four bodies

Timur Ibragimov, Nathan W. C. Leigh, Taeho Ryu, Teresa Panurach, Rosalba Perna
Submitted Wednesday 14 March 2018 @ 18:00:06 GMT
17 pages, 18 figures, 2 tables; accepted for publication in MNRAS

We present a half-life formalism for describing the disruption of gravitationally-boun​d few-body systems, with a focus on binary-binary scattering. For negative total encounter energies, the four-body problem has three possible decay products in the point particle limit. For each decay product and a given set of initial conditions, we obtain directly from numerical scattering simulations the half-life for the distribution of disruption times. As in radioactive decay, the half-lives should provide a direct prediction for the relative fractions of each decay product. We test this prediction with simulated data and find good agreement with our hypothesis. We briefly discuss applications of this feature of the gravitational four-body problem to populations of black holes in globular clusters. This paper, the second in the series, builds on extending the remarkable similarity between gravitational chaos at the macroscopic scale and radioactive decay at the microscopic scale to larger-N systems.

[39] arXiv:1803.05443v1 [pdf, vox]

Quasinormal modes and strong cosmic censorship in near-extremal Kerr-Newman-de Sitter black-hole spacetimes

Shahar Hod
Submitted Wednesday 14 March 2018 @ 18:00:05 GMT
9 pages

The quasinormal resonant modes of massless neutral fields in near-extremal Kerr-Newman-de Sitter black-hole spacetimes are calculated in the eikonal regime. It is explicitly proved that, in the angular momentum regime ${\bar a}> \sqrt{{{1-2{\bar\Lam​bda}}\over{4+{\bar\L​ambda}/3}}}$, the black-hole spacetimes are characterized by slowly decaying resonant modes which are described by the compact formula $\Im\omega(n)=\kappa​_+\cdot(n+{1\over2})​$ [here the physical parameters $\{{\bar a},\kappa_+,{\bar\La​mbda},n\}$ are respectively the dimensionless angular momentum of the black hole, its characteristic surface gravity, the dimensionless cosmological constant of the spacetime, and the integer resonance parameter]. Our results support the validity of the Penrose strong cosmic censorship conjecture in these black-hole spacetimes.

[40] arXiv:1803.05441v1 [pdf, vox]

A Higgsploding Theory of Dark Matter

Valentin V. Khoze, Joey Reiness, Jakub Scholtz, Michael Spannowsky
Submitted Wednesday 14 March 2018 @ 18:00:03 GMT
20 pages, 4 figures

We show that the Higgsplosion mechanism makes a prediction for the mass and coupling of a WIMP-like minimal scalar dark matter model. In particular the currently favoured minimal value for the Higgsplosion scale, $E_\mathrm{H}\sim 25$ TeV, implies a dark matter mass $m_\mathrm{DM} \sim 1.25$ TeV and a moderate quartic coupling with the Standard Model Higgs field $\lambda_\mathrm{H,D​M} \sim 0.4$. This point in the parameter space is still allowed by all current experimental bounds, including direct detection (XENON), indirect detection (HESS, Fermi, Planck) and collider searches. We have updated the scalar dark matter bounds to reflect the latest results from XENON and HESS experiments. We also comment on vacuum stability and dark matter self-interactions in this model.

[41] arXiv:1803.05442v1 [pdf, vox]

Detection of HOCO+ in the protostar IRAS 16293-2422

Liton Majumdar, Pierre Gratier, Valentine Wakelam, Emmanuel Caux, Karen Willacy, Michael E. Ressler
Submitted Wednesday 14 March 2018 @ 18:00:03 GMT
Accepted for publication in MNRAS on March 13th, 7 pages, 3 figures, 2 tables

The protonated form of CO2, HOCO+, is assumed to be an indirect tracer of CO2 in the millimeter/submillim​eter regime since CO2 lacks a permanent dipole moment. Here, we report the detection of two rotational emission lines (4 0,4-3 0,3) and (5 0,5-4 0,4) of HOCO+ in IRAS 16293-2422. For our observations, we have used EMIR heterodyne 3 mm receiver of the IRAM 30m telescope. The observed abundance of HOCO+ is compared with the simulations using the 3-phase NAUTILUS chemical model. Implications of the measured abundances of HOCO+ to study the chemistry of CO2 ices using JWST-MIRI and NIRSpec are discussed as well.

[42] arXiv:1803.05438v1 [pdf, vox]

Exotic Gravitational Wave Signatures from Simultaneous Phase Transitions

Djuna Croon, Graham White
Submitted Wednesday 14 March 2018 @ 18:00:01 GMT
24 pages, 7 figures

We demonstrate that the relic gravitational wave background from a multi-step phase transition may deviate from the simple sum of the single spectra, for phase transitions with similar nucleation temperatures $T_N$. We demonstrate that the temperature range $\Delta T$ between the volume fractions $f(T)=0.1$ and $f(T)=0.9$ occupied by the vacuum bubbles can span $\sim 20$ GeV. This allows for a situation in which phase transitions overlap, such that the later bubbles may nucleate both in high temperature and intermediate temperature phases. Such scenarios may lead to more exotic gravitational wave spectra, which cannot be fitted that of a consecutive PTs. We demonstrate this explicitly in the singlet extension of the Standard Model. Finally, we comment on potential additional effects due to the more exotic dynamics of overlapping phase transitions.

[43] arXiv:1803.05436v1 [pdf, vox]

Evidence for a New Component of High-Energy Solar Gamma-Ray Production

Tim Linden, Bei Zhou, John F. Beacom, Annika H. G. Peter, Kenny C. Y. Ng, Qing-Wen Tang
Submitted Wednesday 14 March 2018 @ 18:00:00 GMT
5 pages, 2 figures. Supplemental Material includes an additional 10 pages, 8 figures. To Be Submitted to Physical Review Letters

The observed multi-GeV gamma-ray emission from the solar disk --- sourced by hadronic cosmic rays interacting with gas, and affected by complex magnetic fields --- is not understood. Utilizing an improved analysis of the Fermi-LAT data that includes the first resolved imaging of the disk, we find strong evidence that this emission is produced by two separate mechanisms. Between 2010-2017 (the rise to and fall from solar maximum), the gamma-ray emission is dominated by a polar component. Between 2008-2009 (solar minimum) this component remains present, but the total emission is instead dominated by a new equatorial component with a brighter flux and harder spectrum. Most strikingly, although 6 gamma rays above 100 GeV are observed during the 1.4 years of solar minimum, none are observed during the next 7.8 years. These features, along with a 30-50 GeV spectral dip which will be discussed in a companion paper, were not anticipated by theory. To understand the underlying physics, Fermi and HAWC observations of the imminent Cycle 25 solar minimum are crucial.

[44] arXiv:1803.05437v1 [pdf, vox]

New constraints on turbulence and embedded planet mass in the HD 163296 disk from planet-disk hydrodynamic simulations

Shang-Fei Liu, Sheng Jin, Shengtai Li, Andrea Isella, Hui Li
Submitted Wednesday 14 March 2018 @ 18:00:00 GMT
13 pages, 8 figures, accepted for publication in ApJ

Recent Atacama Large Millimeter and Submillimeter Array (ALMA) observations of the protoplanetary disk around the Herbig Ae star HD 163296 revealed three depleted dust gaps at 60, 100 and 160 au in the 1.3 mm continuum as well as CO depletion in the middle and outer dust gaps. However, no CO depletion was found in the inner dust gap. To examine the planet--disk interaction model, we present results of two-dimensional two fluid (gas + dust) hydrodynamic simulations coupled with three-dimensional radiative transfer simulations. In order to fit the high gas-to-dust ratio of the first gap, we find the Shakura--Sunyaev viscosity parameter $\alpha$ must be very small ($\lesssim 10^{-4}$) in the inner disk. On the other hand, a relatively large $\alpha$ ($\sim 7.5\times 10^{-3}$) is required to reproduce the dust surface density in the outer disk. We interpret the variation of $\alpha$ as an indicator of the transition from an inner dead zone to the outer magnetorotational instability (MRI) active zone. Within $\sim 100$ au, the HD 163296 disk's ionization level is low, and non-ideal magnetohydrodynamic (MHD) effects could suppress the MRI, so the disk can be largely laminar. The disk's ionization level gradually increases toward larger radii, and the outermost disk ($r > 300$ au) becomes turbulent due to MRI. Under this condition, we find that the observed dust continuum and CO gas line emissions can be reasonably fit by three half-Jovian-mass planets (0.46, 0.46 and 0.58 $M_\textrm{J}$) at 59, 105 and 160 au, respectively.

[45] arXiv:1803.05425v1 [pdf, vox]

Discovery of a new classical nova shell around a nova-like cataclysmic variable

Martin A. Guerrero, Laurence Sabin, Gagik Tovmassian, Edgar Santamaria, Raul Michel, Gerardo Ramos-Larios, Alexandre Alarie, Christophe Morisset, Luis C. Bermudez Bustamante, Chantal P. Gonzalez, Nick J. Wright
Submitted Wednesday 14 March 2018 @ 17:58:41 GMT
Accepted for publication in The Astrophysical Journal: 3 tables, 12 figures

The morphology and optical spectrum of IPHASXJ210205+471015​, a nebula classified as a possible planetary nebula, are however strikingly similar to those of ATCnc, a classical nova shell around a dwarf nova. To investigate its true nature, we have obtained high-resolution narrow-band [O III] and [N II] images and deep GTC OSIRIS optical spectra. The nebula shows an arc of [N II]-bright knots notably enriched in nitrogen, whilst an [O III]-bright bow-shock is progressing throughout the ISM. Diagnostic line ratios indicate that shocks are associated with the arc and bow-shock. The central star of this nebula has been identified by its photometric variability. Time-resolved photometric and spectroscopic data of this source reveal a period of 4.26 hours, which is attributed to a binary system. The optical spectrum is notably similar to that of RWSex, a cataclysmic variable star (CV) of the UXUMa nova-like (NL) type. Based on these results, we propose that IPHASX J210205+471015 is a classical nova shell observed around a CV-NL system in quiescence.

[46] arXiv:1803.05424v1 [pdf, vox]

Warm FIRE: Simulating Galaxy Formation with Resonant Sterile Neutrino Dark Matter

Brandon Bozek, Alex Fitts, Michael Boylan-Kolchin, Shea Garrison-Kimmel, Kevork Abazajian, James S. Bullock, Dusan Keres, Claude-Andre Faucher-Giguere, Andrew Wetzel, Robert Feldmann, Philip F. Hopkins
Submitted Wednesday 14 March 2018 @ 17:57:33 GMT
15 pages, 8 figures, 1 table; submitted to MNRAS

We study the impact of a warm dark matter (WDM) cosmology on dwarf galaxy formation through a suite of cosmological hydrodynamical zoom-in simulations of $M_{\rm halo} \approx10^{10}\,M_{\​odot}$ dark matter halos as part of the Feedback in Realistic Environments (FIRE) project. A main focus of this paper is to evaluate the combined effects of dark matter physics and stellar feedback on the well-known small-scale issues found in cold dark matter (CDM) models. We find that the $z=0$ stellar mass of a galaxy is strongly correlated with the central density of its host dark matter halo at the time of formation, $z_{\rm f}$, in both CDM and WDM models. WDM halos follow the same $M_{\star}(z=0)-V_{\​rm max}(z_{\rm f})$ relation as in CDM, but they form later, are less centrally dense, and therefore contain galaxies that are less massive than their CDM counterparts. As a result, the impact of baryonic effects on the central gravitational potential is typically diminished relative to CDM. However, the combination of delayed formation in WDM and energy input from stellar feedback results in dark matter profiles with lower overall densities. The WDM galaxies studied here have a wider diversity of star formation histories (SFHs) than the same systems simulated in CDM, and the two lowest $M_{\star}$ WDM galaxies form all of their stars at late times. The discovery of young ultra-faint dwarf galaxies with no ancient star formation -- which do not exist in our CDM simulations -- would therefore provide evidence in support of WDM.

[47] arXiv:1803.05390v1 [pdf, vox]

Computational Techniques for the Analysis of Small Signals in High-Statistics Neutrino Oscillation Experiments

IceCube-Gen2 Collaboration, :, M. G. Aartsen, M. Ackermann, J. Adams, J. A. Aguilar, M. Ahlers, M. Ahrens, I. Al Samarai, D. Altmann, K. Andeen, T. Anderson, I. Ansseau, G. Anton, C. Argüelles, T. C. Arlen, J. Auffenberg, S. Axani, H. Bagherpour, X. Bai, A. V. Balagopal, J. P. Barron, I. Bartos, S. W. Barwick, V. Baum, R. Bay, J. J. Beatty, J. Becker Tjus, K. -H. Becker, S. BenZvi, D. Berley, E. Bernardini, D. Z. Besson, G. Binder, D. Bindig, E. Blaufuss, S. Blot, C. Bohm, M. Bohmer, M. Börner, F. Bos, S. Böser, O. Botner, E. Bourbeau, J. Bourbeau, F. Bradascio, J. Braun, M. Brenzke, H. -P. Bretz, S. Bron, J. Brostean-Kaiser, A. Burgman, R. S. Busse, T. Carver, E. Cheung, D. Chirkin, A. Christov, K. Clark, L. Classen, G. H. Collin, J. M. Conrad, P. Coppin, P. Correa, D. F. Cowen, R. Cross, P. Dave, M. Day, J. P. A. M. de André, C. De Clercq, J. J. DeLaunay, H. Dembinski, S. De Ridder, P. Desiati, K. D. de Vries, G. de Wasseige, M. de With, T. DeYoung, J. C. Díaz-Vélez, V. di Lorenzo, H. Dujmovic, J. P. Dumm, M. Dunkman, M. A. DuVernois, E. Dvorak, B. Eberhardt, T. Ehrhardt, B. Eichmann, P. Eller, R. Engel, J. J. Evans, P. A. Evenson, S. Fahey, A. R. Fazely, J. Felde, K. Filimonov, C. Finley, S. Flis, A. Franckowiak, E. Friedman, A. Fritz, T. K. Gaisser, J. Gallagher, A. Gartner, L. Gerhardt, R. Gernhaeuser, K. Ghorbani, W. Giang, T. Glauch, T. Glüsenkamp, A. Goldschmidt, J. G. Gonzalez, D. Grant, Z. Griffith, C. Haack, A. Hallgren, F. Halzen, K. Hanson, J. Haugen, A. Haungs, D. Hebecker, D. Heereman, K. Helbing, R. Hellauer, F. Henningsen, S. Hickford, J. Hignight, G. C. Hill, K. D. Hoffman, B. Hoffmann, R. Hoffmann, T. Hoinka, B. Hokanson-Fasig, K. Holzapfel, K. Hoshina, F. Huang, M. Huber, T. Huber, T. Huege, K. Hultqvist, M. Hünnefeld, R. Hussain, S. In, N. Iovine, A. Ishihara, E. Jacobi, G. S. Japaridze, M. Jeong, K. Jero, B. J. P. Jones, P. Kalaczynski, O. Kalekin, W. Kang, D. Kang, A. Kappes, D. Kappesser, T. Karg, A. Karle, T. Katori, U. Katz, M. Kauer, A. Keivani, J. L. Kelley, A. Kheirandish, J. Kim, M. Kim, T. Kintscher, J. Kiryluk, T. Kittler, S. R. Klein, R. Koirala, H. Kolanoski, L. Köpke, C. Kopper, S. Kopper, J. P. Koschinsky, D. J. Koskinen, M. Kowalski, C. B. Krauss, K. Krings, M. Kroll, G. Krückl, S. Kunwar, N. Kurahashi, T. Kuwabara, A. Kyriacou, M. Labare, J. L. Lanfranchi, M. J. Larson, F. Lauber, D. Lennarz, K. Leonard, M. Lesiak-Bzdak, A. Leszczynska, M. Leuermann, Q. R. Liu, E. Lohfink, J. LoSecco, C. J. Lozano Mariscal, L. Lu, J. Lünemann, W. Luszczak, J. Madsen, G. Maggi, K. B. M. Mahn, S. Mancina, S. Mandalia, S. Marka, Z. Marka, R. Maruyama, K. Mase, R. Maunu, K. Meagher, M. Medici, M. Meier, T. Menne, G. Merino, T. Meures, S. Miarecki, J. Micallef, G. Momenté, T. Montaruli, R. W. Moore, M. Moulai, R. Nahnhauer, P. Nakarmi, U. Naumann, G. Neer, H. Niederhausen, S. C. Nowicki, D. R. Nygren, A. Obertacke Pollmann, M. Oehler, A. Olivas, A. O'Murchadha, E. O'Sullivan, A. Palazzo, T. Palczewski, H. Pandya, D. V. Pankova, L. Papp, P. Peiffer, J. A. Pepper, C. Pérez de los Heros, T. C. Petersen, D. Pieloth, E. Pinat, J. L. Pinfold, M. Plum, P. B. Price, G. T. Przybylski, C. Raab, L. Rädel, M. Rameez, L. Rauch, K. Rawlins, I. C. Rea, R. Reimann, B. Relethford, M. Relich, M. Renschler, E. Resconi, W. Rhode, M. Richman, M. Riegel, S. Robertson, M. Rongen, C. Rott, T. Ruhe, D. Ryckbosch, D. Rysewyk, I. Safa, T. Sälzer, S. E. Sanchez Herrera, A. Sandrock, J. Sandroos, P. Sandstrom, M. Santander, S. Sarkar, S. Sarkar, K. Satalecka, H. Schieler, P. Schlunder, T. Schmidt, A. Schneider, S. Schoenen, S. Schöneberg, F. G. Schröder, L. Schumacher, S. Sclafani, D. Seckel, S. Seunarine, M. H. Shaevitz, J. Soedingrekso, D. Soldin, S. Söldner-Rembold, M. Song, G. M. Spiczak, C. Spiering, J. Stachurska, M. Stamatikos, T. Stanev, A. Stasik, R. Stein, J. Stettner, A. Steuer, T. Stezelberger, R. G. Stokstad, A. Stößl, N. L. Strotjohann, T. Stuttard, G. W. Sullivan, M. Sutherland, I. Taboada, A. Taketa, H. K. M. Tanaka, J. Tatar, F. Tenholt, S. Ter-Antonyan, A. Terliuk, S. Tilav, P. A. Toale, M. N. Tobin, C. Tönnis, S. Toscano, D. Tosi, M. Tselengidou, C. F. Tung, A. Turcati, C. F. Turley, B. Ty, E. Unger, M. Usner, J. Vandenbroucke, W. Van Driessche, D. van Eijk, N. van Eijndhoven, S. Vanheule, J. van Santen, D. Veberic, E. Vogel, M. Vraeghe, C. Walck, A. Wallace, M. Wallraff, F. D. Wandler, N. Wandkowsky, A. Waza, C. Weaver, A. Weindl, M. J. Weiss, C. Wendt, J. Werthebach, S. Westerhoff, B. J. Whelan, K. Wiebe, C. H. Wiebusch, L. Wille, D. R. Williams, L. Wills, M. Wolf, J. Wood, T. R. Wood, E. Woolsey, K. Woschnagg, G. Wrede, S. Wren, D. L. Xu, X. W. Xu, Y. Xu, J. P. Yanez, G. Yodh, S. Yoshida, T. Yuan
Submitted Wednesday 14 March 2018 @ 16:38:21 GMT

The current and upcoming generation of Very Large Volume Neutrino Telescopes - collecting unprecedented quantities of neutrino events - can be used to explore subtle effects in oscillation physics, such as (but not restricted to) the neutrino mass ordering. The sensitivity of an experiment to these effects can be estimated from Monte Carlo simulations. With the very high number of events that will be collected, there is a trade-off between the computational expense of running such simulations and the inherent statistical uncertainty in the determined values. In such a scenario, it becomes impractical to produce and use adequately-sized sets of simulated events to use with traditional methods, such as Monte Carlo weighting. In this work we present a staged approach to the generation of binned event distributions in order to overcome these challenges. By combining multiple integration and smoothing techniques which address limited statistics from simulation it arrives at reliable analysis results using modest computational resources.

[48] arXiv:1803.05375v1 [pdf, vox]

Surface Composition of (99942) Apophis

Vishnu Reddy, Juan Sanchez, Roberto Furfaro, Richard Binzel, Thomas Burbine, Lucille Le Corre, Paul Hardersen, William Bottke, Marina Brozovic
Submitted Wednesday 14 March 2018 @ 15:55:57 GMT

On April 13, 2029, near-Earth asteroid (NEA) (99942) Apophis will pass at a distance of 6 Earth radii from Earth. This event will provide researchers with a unique opportunity to study the effects of tidal forces experienced by an asteroid during a close encounter with a terrestrial planet. Binzel et al. (2010) predicted that close flybys of terrestrial planets by NEAs would cause resurfacing of their regolith due to seismic shaking. In this work we present the best pre-encounter near-infrared spectra of Apophis obtained so far. These new data were obtained during the 2013 apparition using the NASA Infrared Telescope Facility (IRTF). We found that our spectral data is consistent with previous observations by Binzel et al. (2009) but with a much higher signal-to-noise ratio. Spectral band parameters were extracted from the spectra and were used to determine the composition of the asteroid. Using a naive Bayes classifier, we computed the likelihood of Apophis being an LL chondrite to be >99% based on mol% of Fa vs. Fs. Using the same method, we estimated a probability of 89% for Apophis being an LL chondrite based on ol/(ol+px) and Fs. The results from the dynamical model indicate that the most likely source region for Apophis is the nu6 resonance in the inner main belt. Data presented in this study (especially Band I depth) could serve as a baseline to verify seismic shaking during the 2029 encounter.

[49] arXiv:1803.05715v1 [pdf, vox]

On the jet properties of the gamma-ray loud active galactic nuclei

Liang Chen
Submitted Wednesday 14 March 2018 @ 15:50:43 GMT
Accepted by ApJS, 11 figures, 2 tables. arXiv admin note: text overlap with arXiv:1509.08710, arXiv:1304.6680 by other authors

Based on broadband SEDs, we estimate jet physical parameters of 1392 $\gamma$-ray loud active galactic nuclei (AGNs), the largest sample so far. The (SED) jet power and magnetization parameter are derived for these AGNs. Out of these sources, accretion disk luminosity of 232 sources and (extended) kinetic jet powers of 159 sources are compiled from archived papers. We find, 1) FSRQs and BL Lacs are well separated by $\Gamma=-0.127\log L_{\gamma}+8.18$, in $\gamma$-ray luminosity versus photon index plane, with a succuss rate 88.6\%. 2) Most FSRQs present the (SED) jet power larger than accretion power, which suggests that the relativistic jet launching mechanism is dominated by the Blandford-Znajek process. This result confirms previous finding. 3) We find a significant anti-correlation between jet magnetization and a ratio of the (SED) jet power to the (extended) kinetic jet power, which, for the first time, provides supporting evidence for jet energy transportation theory: high magnetization jet may be more easily to transport energy to large scale than low magnetization jet.

[50] arXiv:1803.05354v1 [pdf, vox]

Observations of fast-moving features in the debris disk of AU Mic on a three-year timescale: Confirmation and new discoveries

A. Boccaletti, E. Sezestre, A. -M. Lagrange, P. Thébault, R. Gratton, M. Langlois, C. Thalmann, M. Janson, P. Delorme, J. -C. Augereau, G. Schneider, J. Milli, C. Grady, J. Debes, Q. Kral, J. Olofsson, J. Carson, A. L. Maire, T. Henning, J. Wisniewski, J. Schlieder, C. Dominik, S. Desidera, C. Ginski, D. Hines, F. Ménard, D. Mouillet, N. Pawellek, A. Vigan, E. Lagadec, H. Avenhaus, J. -L. Beuzit, B. Biller, M. Bonavita, M. Bonnefoy, W. Brandner, F. Cantalloube, G. Chauvin, A. Cheetham, M. Cudel, C. Gry, S. Daemgen, M. Feldt, R. Galicher, J. Girard, P. Janin-Potiron, M. Kasper, H. Le Coroller, D. Mesa, S. Peretti, C. Perrot, M. Samland, E. Sissa, F. Wildi, S. Rochat, E. Stadler, L. Gluck, A. Origné, M. Llored, P. Baudoz, G. Rousset, P. Martinez, F. Rigal
Submitted Wednesday 14 March 2018 @ 15:29:51 GMT
23 pages, 20 figures, accepted for publication in Astronomy and Astrophysics

The nearby and young M star AU Mic is surrounded by a debris disk in which we previously identified a series of large-scale arch-like structures that have never been seen before in any other debris disk and that move outward at high velocities. We initiated a monitoring program with the following objectives: 1) track the location of the structures and better constrain their projected speeds, 2) search for new features emerging closer in, and ultimately 3) understand the mechanism responsible for the motion and production of the disk features. AU Mic was observed at 11 different epochs between August 2014 and October 2017 with the IR camera and spectrograph of SPHERE. These high-contrast imaging data were processed with a variety of angular, spectral, and polarimetric differential imaging techniques to reveal the faintest structures in the disk. We measured the projected separations of the features in a systematic way for all epochs. We also applied the very same measurements to older observations from the Hubble Space Telescope (HST) with the visible cameras STIS and ACS. The main outcomes of this work are 1) the recovery of the five southeastern broad arch-like structures we identified in our first study, and confirmation of their fast motion (projected speed in the range 4-12 km/s); 2) the confirmation that the very first structures observed in 2004 with ACS are indeed connected to those observed later with STIS and now SPHERE; 3) the discovery of two new very compact structures at the northwest side of the disk (at 0.40" and 0.55" in May 2015) that move to the southeast at low speed; and 4) the identification of a new arch-like structure that might be emerging at the southeast side at about 0.4" from the star (as of May 2016). Abridged.

[51] arXiv:1803.04444v2 [pdf, vox]

Formation and evolution of hybrid He-CO white dwarfs and their properties

Yossef Zenati, Silvia Toonen, Hagai B. Perets
Submitted Wednesday 14 March 2018 @ 15:19:18 GMT
9 pages, 12 figures,, 1 table, Submitted to MNRAS

White dwarfs (WDs) are the stellar core remnants of low mass stars. They are typically divided into three main composition groups: Oxygen Neon (ONe), Carbon Oxygen (CO) and Helium (He) WDs. The evolution of binary systems can significantly change the evolution of the binary stellar components. In particular, striping the envelope of an evolved star can give rise to a core remnant, which can later evolve into a WD with significantly different composition. Here we focus on the formation and evolution of hybrid HeCO WDs. We follow the formation and stellar evolution of such WDs for a range of initial conditions and provide their detailed structure, mass-radius relation and luminosity temperature evolution. We find that both low mass WDs (< 0.45M , typically thought to be He WDs) and intermediate-mass WDs (0.45 < MWD < 0.7, typically thought to be CO WDs) could in fact be hybrid HeCO WDs, with 5-25 (75 -95)% of their mass in He (CO). We use population synthesis calculations to infer the birth rate and properties of such WDs. We find that hybrid HeCO WD comprise the majority of young (< 2Gyr) WDs in binaries, but are more rare among older WDs in binaries. The high frequency and large He content of such WDs could have an important role in WD WD mergers, and may give rise to sub Chandrasekhar thermonuclear supernova explosions.

[52] arXiv:1803.05327v1 [pdf, vox]

Model-independent exoplanet transit spectroscopy

Erik Aronson, Nikolai Piskunov
Submitted Wednesday 14 March 2018 @ 14:54:15 GMT

We propose a new data analysis method for obtaining transmission spectra of exoplanet atmospheres and brightness variation across the stellar disk from transit observations. The new method is capable of recovering exoplanet atmosphere absorption spectra and stellar specific intensities without relying on theoretical models of stars and planets. We fit both stellar specific intensity and planetary radius simultaneously directly to transit light curves. This allows stellar models to be removed from the data analysis. Furthermore, we use a data-quality weighted filtering technique to achieve an optimal trade-off between spectral resolution and reconstruction fidelity homogenising the signal to noise ratio across the wavelength range. Such approach is more efficient than conventional data binning onto a low resolution wavelength grid. We demonstrate that our analysis is capable of re-producing results achieved by using explicit quadratic limb darkening equation, and that the filtering technique helps eliminating spurious spectral features in regions with strong telluric absorption. The method is applied to the VLT FORS2 observations of the exoplanets GJ 1214 b and WASP-49 b, and our results are in agreement with previous studies. Comparisons between obtained stellar specific intensity and numerical models indicates that the method is capable of accurately reconstructing the specific intensity. The proposed method enables more robust characterization of exoplanetary atmospheres by separating derivation of planetary transmission and stellar specific intensity spectra (that is model-independent) from chemical and physical interpretation.

[53] arXiv:1803.05305v1 [pdf, vox]

Resonance Capture and Dynamics of 3-Planet Systems

C. Charalambous, J. G. Martí, C. Beaugé, X. S. Ramos
Submitted Wednesday 14 March 2018 @ 14:24:41 GMT

We present a series of dynamical maps for fictitious 3-planets systems in initially circular coplanar orbits. These maps have unveiled a rich resonant structure involving two or three planets, as well as indicating possible migration routes from secular to double resonances or pure 3-planet commensurabilities. These structures are then compared to the present-day orbital architecture of observed resonant chains. In a second part of the paper we describe N-body simulations of type-I migration. Depending on the orbital decay timescale, we show that 3-planet systems may be trapped in different combinations of independent commensurabilities: (i) double resonances, (ii) intersection between a 2-planet and a first-order 3-planet resonance, and (iii) simultaneous libration in two first-order 3-planet resonances. These latter outcomes are found for slow migrations, while double resonances are almost always the final outcome in high-density disks. Finally, we discuss an application to the TRAPPIST-1 system. We find that, for low migration rates and planetary masses of the order of the estimated values, most 3-planet sub-systems are able to reach the observed double resonances after following evolutionary routes defined by pure 3-planet resonances. The final orbital configuration shows resonance offsets comparable with present-day values without the need of tidal dissipation. For the 8/5 resonance proposed to dominate the dynamics of the two inner planets, we find little evidence of its dynamical significance; instead, we propose that this relation between mean motions could be a consequence of the interaction between a pure 3-planet resonance and a 2-planet commensurability between planets c and d.

[54] arXiv:1803.05300v1 [pdf, vox]

Accelerating infall and rotational spin-up in the hot molecular core G31.41+0.31

M. T. Beltrán, R. Cesaroni, V. M. Rivilla, Á. Sánchez-Monge, L. Moscadelli, A. Ahmadi, V. Allen, H. Beuther, S. Etoka, D. Galli, R. Galván-Madrid, C. Goddi, K. G. Johnston, A. Kölligan, R. Kuiper, M. S. N. Kumar, L. T. Maud, J. C. Mottram, T. Peters, P. Schilke, L. Testi
Submitted Wednesday 14 March 2018 @ 14:21:14 GMT
28 pages, 16 figures, and 7 tables. Accepted for publication in A&A

As part of our effort to search for circumstellar disks around high-mass stellar objects, we observed the well-known core G31.41+0.31 with ALMA at 1.4 mm with an angular resolution of~0.22" (~1700 au). The dust continuum emission has been resolved into two cores namely Main and NE. The Main core, which has the stronger emission and is the more chemically rich, has a diameter of ~5300 au, and is associated with two free-free continuum sources. The Main core looks featureless and homogeneous in dust continuum emission and does not present any hint of fragmentation. Each transition of CH3CN and CH3OCHO, both ground and vibrationally excited, as well as those of CH3CN isotopologues, shows a clear velocity gradient along the NE-SW direction, with velocity linearly increasing with distance from the center, consistent with solid-body rotation. However, when comparing the velocity field of transitions with different upper level energies, the rotation velocity increases with increasing energy of the transition, which suggests that the rotation speeds up towards the center. Spectral lines towards the dust continuum peak show an inverse P-Cygni profile that supports the existence of infall in the core. The infall velocity increases with the energy of the transition suggesting that the infall is accelerating towards the center of the core, consistent with gravitational collapse. Despite the monolithic appearance of the Main core, the presence of red-shifted absorption, the existence of two embedded free-free sources at the center, and the rotational spin-up are consistent with an unstable core undergoing fragmentation with infall and differential rotation due to conservation of angular momentum. Therefore, the most likely explanation for the monolithic morphology is that the large opacity of the dust emission prevents the detection of any inhomogeneity in the core.

[55] arXiv:1803.05285v1 [pdf, vox]

An Acoustical Analogue of a Galactic-scale Gravitational-Wave Detector

Michael T. Lam, Joseph D. Romano, Joey S. Key, Marc Normandin, Jeffrey S. Hazboun
Submitted Wednesday 14 March 2018 @ 14:01:24 GMT
21 pages, 9 figures, submitted to the American Journal of Physics

By precisely monitoring the "ticks" of Nature's most precise clocks (millisecond pulsars), scientists are trying to detect the "ripples in spacetime" (gravitational waves) produced by the inspirals of supermassive black holes in the centers of distant merging galaxies. Here we describe a relatively simple demonstration that uses two metronomes and a microphone to illustrate several techniques used by pulsar astronomers to search for gravitational waves. An adapted version of this demonstration could be used as an instructional laboratory investigation at the undergraduate level.

[56] arXiv:1803.05251v1 [pdf, vox]

The Local Bubble: a magnetic veil to our Galaxy

M. I. R. Alves, F. Boulanger, K. Ferriere, L. Montier
Submitted Wednesday 14 March 2018 @ 13:07:12 GMT
5 pages (plus 1 page Appendix), 2 figures, Accepted for publications in A&A Letters

The magnetic field in the local interstellar medium does not follow the large-scale Galactic magnetic field. The local magnetic field has probably been distorted by the Local Bubble, a cavity of hot ionized gas extending all around the Sun and surrounded by a shell of cold neutral gas and dust. However, so far no conclusive association between the local magnetic field and the Local Bubble has been established. Here we develop an analytical model for the magnetic field in the shell of the Local Bubble, which we represent as an inclined spheroid, off-centred from the Sun. We fit the model to Planck dust polarized emission observations within 30 deg of the Galactic poles. We find a solution that is consistent with a highly deformed magnetic field, with significantly different directions towards the north and south Galactic poles. This work sets a methodological framework for modelling the three-dimensional (3D) structure of the magnetic field in the local interstellar medium, which is a most awaited input for large-scale Galactic magnetic field models.

[57] arXiv:1803.05238v1 [pdf, vox]

A Likely Detection of a Two-Planet System in a Low Magnification Microlensing Event

D. Suzuki, D. P. Bennett, A. Udalski, I. A. Bond, T. Sumi, C. Han, F. Abe, Y. Asakura, R. K. Barry, A. Bhattacharya, M. Donachie, M. Freeman, A. Fukui, Y. Hirao, Y. Itow, N. Koshimoto, M. C. A. Li, C. H. Ling, K. Masuda, Y. Matsubara, Y. Muraki, M. Nagakane, K. Onishi, H. Oyokawa, C. Ranc, N. J. Rattenbury, To. Saito, A. Sharan, D. J. Sullivan, P. J. Tristram, A. Yonehara, R. Poleski, P. Mróz, J. Skowron, M. K. Szymański, I. Soszyński, S. Kozłowski, P. Pietrukowicz, Ł. Wyrzykowski, K. Ulaczyk
Submitted Wednesday 14 March 2018 @ 12:33:32 GMT
Submitted to AAS

We report on the analysis of a microlensing event OGLE-2014-BLG-1722 that showed two distinct short term anomalies. The best fit model to the observed light curves shows that the two anomalies are explained with two planetary mass ratio companions to the primary lens. Although a binary source model is also able to explain the second anomaly, it is marginally ruled out by 3.1 $\sigma$. The 2-planet model indicates that the first anomaly was caused by planet "b" with a mass ratio of $q = (4.5_{-0.6}^{+0.7}) \times 10^{-4}$ and projected separation in unit of the Einstein radius, $s = 0.753 \pm 0.004$. The second anomaly reveals planet "c" with a mass ratio of $q_{2} = (7.0_{-1.7}^{+2.3}) \times 10^{-4}$ with $\Delta \chi^{2} \sim 170$ compared to the single planet model. Its separation has a so-called close-wide degeneracy. We estimated the physical parameters of the lens system from Bayesian analysis. This gives that the masses of planet b and c are $m_{\rm b} = 56_{-33}^{+51}\,M_{\​oplus}$ and $m_{\rm c} = 85_{-51}^{+86}\,M_{\​oplus}$, respectively, and they orbit a late type star with a mass of $M_{\rm host} = 0.40_{-0.24}^{+0.36}​\,M_{\odot}$ located at $D_{\rm L} = 6.4_{-1.8}^{+1.3}\,\​rm kpc$ from us. If the 2-planet model is true, this is the third multiple planet system detected by using the microlensing method, and the first multiple planet system detected in the low magnification events, which are dominant in the microlensing survey data. The occurrence rate of multiple cold gas giant systems is estimated using the two such detections and a simple extrapolation of the survey sensitivity of 6 year MOA microlensing survey (Suzuki et al. 2016) combined with the 4 year $\mu$FUN detection efficiency (Gould et al. 2010). It is estimated that $6 \pm 2\,\%$ of stars host two cold giant planets.

[58] arXiv:1803.05237v1 [pdf, vox]

Blue wing enhancement of the chromospheric Mg II h and k lines in a solar flare

Akiko Tei, Takahito Sakaue, Tekanori J. Okamoto, Tomoko Kawate, Petr Heinzel, Satoru Ueno, Ayumi Asai, Kiyoshi Ichimoto, Kazunari Shibata
Submitted Wednesday 14 March 2018 @ 12:32:13 GMT
19 pages, 13 figures, accepted for publication in PASJ

We performed coordinated observations of AR 12205, which produced a C-class flare on 2014 November 11, with the Interface Region Imaging Spectrograph (IRIS) and the Domeless Solar Telescope (DST) at Hida Observatory. Using spectral data in the Si IV 1403 \AA, C II 1335 \AA, and Mg II h and k lines from IRIS and the Ca II K, Ca II 8542 \AA, and H$\alpha$ lines from DST, we investigated a moving flare kernel during the flare. In the Mg II h line, the leading edge of the flare kernel showed the intensity enhancement in the blue wing, and the smaller intensity of the blue-side peak (h2v) than that of the red-side one (h2r). The blueshift lasted for 9-48 s with a typical speed of 10.1 $\pm$ 2.6 km s$^{-1}$ and it was followed by the high intensity and the large redshift with a speed of up to 51 km s$^{-1}$ detected in the Mg II h line. The large redshift was a common property for all six lines but the blueshift prior to it was found only in the Mg II lines. A cloud modeling of the Mg II h line suggests that the blue wing enhancement with such peak difference can be caused by a chromospheric-temper​ature (cool) upflow. We discuss a scenario in which an upflow of cool plasma is lifted up by expanding hot plasma owing to the deep penetration of non-thermal electrons into the chromosphere. Furthermore, we found that the blueshift persisted without any subsequent redshift in the leading edge of the flare kernel during its decaying phase. The cause of such long-lasting blueshift is also discussed.

[59] arXiv:1803.05230v1 [pdf, vox]

Simplified models of circumstellar morphologies for interpreting high-resolution data. Analytical approach to the equatorial density enhancement

Ward Homan, Jels Boulangier, Leen Decin, Alex de Koter
Submitted Wednesday 14 March 2018 @ 12:19:03 GMT

Equatorial density enhancements (EDEs) are a very common astronomical phenomenon. Studies of the circumstellar environments (CSE) of young stellar objects and of evolved stars have shown that these objects often possess these features. These are believed to originate from different mechanisms, ranging from binary interactions to the gravitational collapse of interstellar material. Quantifying the effect of the presence of this type of EDE on the observables is essential for a correct interpretation of high-resolution data. We seek to investigate the manifestation in the observables of a circumstellar EDE, to assess which properties can be constrained, and to provide an intuitive bedrock on which to compare and interpret upcoming high-resolution data (e.g. \emph{ALMA} data) using 3D models. We develop a simplified analytical parametrised description of a 3D EDE, with a possible substructure such as warps, gaps, and spiral instabilities. In addition, different velocity fields (Keplerian, radial, super-Keplerian, sub-Keplerian and rigid rotation) are considered. The effect of a bipolar outflow is also investigated. The geometrical models are fed into the 3D radiative transfer code {\tt LIME}, that produces 3D intensity maps throughout velocity space. We investigate the spectral signature of the $J$=3$-$2 up to $J$=7$-$6 rotational transitions of CO in the models, as well as the spatial aspect of this emission by means of channel maps, wide-slit position-velocity (PV) diagrams, stereograms, and spectral lines. Additionally, we discuss methods of constraining the geometry of the EDE, the inclination, the mass-contrast between the EDE and the bipolar outflow, and the global velocity field. Finally, we simulated \emph{ALMA} observations...

[60] arXiv:1803.05228v1 [pdf, vox]

Ultra High Molecular Weight Polyethylene: optical features at millimeter wavelengths

G. D'Alessandro, A. Paiella, A. Coppolecchia, M. G. Castellano, I. Colantoni, P. de Bernardis, L. Lamagna, S. Masi
Submitted Wednesday 14 March 2018 @ 12:15:26 GMT

The next generation of experiments for the measurement of the Cosmic Microwave Background (CMB) requires more and more the use of advanced materials, with specific physical and structural properties. An example is the material used for receiver's cryostat windows and internal lenses. The large throughput of current CMB experiments requires a large diameter (of the order of 0.5m) of these parts, resulting in heavy structural and optical requirements on the material to be used. Ultra High Molecular Weight (UHMW) polyethylene (PE) features high resistance to traction and good transmissivity in the frequency range of interest. In this paper, we discuss the possibility of using UHMW PE for windows and lenses in experiments working at millimeter wavelengths, by measuring its optical properties: emissivity, transmission and refraction index. Our measurements show that the material is well suited to this purpose.

[61] arXiv:1803.05222v1 [pdf, vox]

ALMA observations of the nearby AGB star L$_{\rm 2}$ Puppis. II. Gas disk properties derived from $^{\rm 12}$CO and $^{\rm13}$CO $J=$3$-$2 emission

Ward Homan, Anita Richards, Leen Decin, Pierre Kervella, Alex de Koter, Iain McDonald, Keiichi Ohnaka
Submitted Wednesday 14 March 2018 @ 11:54:06 GMT
21 pages; 19 figures

The circumstellar environment of the AGB star L$_{\rm 2}$ Puppis was observed with ALMA in cycle 3, with a resolution of $15 \times 18 \rm\ mas$. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series (paper I) the molecular emission was analysed to accurately deduce the motion of the gas in the equatorial regions of the disk. In this work we model the optically thick $^{\rm 12}$CO $J=$3$-$2 and the optically thin $^{\rm 13}$CO $J=$3$-$2 rotational transition to constrain the physical conditions in the disk. To realise this effort we make use of the 3D NLTE radiative transfer code {\tt LIME}. The temperature structure and velocity structure show a high degree of complexity, both radially and vertically. The radial H$_{\rm 2}$ density profile in the disk plane is characterised by a power law with a slope of $-3.1$. We find a $^{\rm 12}$CO over $^{\rm 13}$CO abundance ratio of 10 inside the disk. Finally, estimations of the angular momentum in the disk surpass the expected available angular momentum of the star, strongly supporting the indirect detection of a compact binary companion reported in paper I. We estimate the mass of the companion to be around 1 Jupiter mass.

[62] arXiv:1803.05203v1 [pdf, vox]

The propagating speed of relic gravitational waves and their refractive index during inflation

Massimo Giovannini
Submitted Wednesday 14 March 2018 @ 11:09:52 GMT
31 pages, 12 figures

If the refractive index of the tensor modes increases during a conventional inflationary stage of expansion the relic graviton spectrum is tilted towards high frequencies. Two apparently diverse parametrizations of this effect are shown to be related by a rescaling of the four-dimensional metric through a conformal factor that involves the refractive index itself. Non-monotonic spectra with a maximum in the MHz region correspond to a limited variation of the refractive index terminating well before the end of inflation. After exploring a general approach encompassing the ones proposed so far, we estimate the required sensitivity for the direct detection of the predicted gravitational radiation and demonstrate that the allowed regions of the parameter space are within reach for some of the planned detectors operating either in the audio band (like Ligo/Virgo and Kagra) or in the mHz band (like Lisa, Bbo and Decigo).

[63] arXiv:1803.05195v1 [pdf, vox]

Finite amplitude transverse oscillations of a magnetic rope

Dmitrii Y. Kolotkov, Giuseppe Nistico, George Rowlands, Valery M. Nakariakov
Submitted Wednesday 14 March 2018 @ 10:35:48 GMT

The effects of finite amplitudes on the transverse oscillations of a quiescent prominence represented by a magnetic rope are investigated in terms of the model proposed by Kolotkov et al. 2016. We consider a weakly nonlinear case governed by a quadratic nonlinearity, and also analyse the fully nonlinear equations of motion. We treat the prominence as a massive line current located above the photosphere and interacting with the magnetised dipped environment via the Lorentz force. In this concept the magnetic dip is produced by two external current sources located at the photosphere. Finite amplitude horizontal and vertical oscillations are found to be strongly coupled between each other. The coupling is more efficient for larger amplitudes and smaller attack angles between the direction of the driver and the horizontal axis. Spatial structure of oscillations is represented by Lissajous-like curves with the limit cycle of a hourglass shape, appearing in the resonant case, when the frequency of the vertical mode is twice the horizontal mode frequency. A metastable equilibrium of the prominence is revealed, which is stable for small amplitude displacements, and becomes horizontally unstable, when the amplitude exceeds a threshold value. The maximum oscillation amplitudes are also analytically derived and analysed. Typical oscillation periods are determined by the oscillation amplitude, prominence current, its mass and position above the photosphere, and the parameters of the magnetic dip. The main new effects of the finite amplitude are the coupling of the horizontally and vertically polarised transverse oscillations (i.e. the lack of a simple, elliptically polarised regime) and the presence of metastable equilibria of prominences.

[64] arXiv:1803.05179v1 [pdf, vox]

Transmission Spectroscopy with the ACE-FTS Infrared Spectral Atlas of Earth: A Model Validation and Feasibility Study

Franz Schreier, Steffen Städt, Pascal Hedelt, Mareike Godolt
Submitted Wednesday 14 March 2018 @ 09:54:24 GMT
25 pages, 15 figures, 3 tables

Infrared solar occultation measurements are well established for remote sensing of Earth's atmosphere, and the corresponding primary transit spectroscopy has turned out to be valuable for characterization of extrasolar planets. Our objective is an assessment of the detectability of molecular signatures in Earth's transit spectra. To this end, we take a limb sequence of representative cloud-free transmission spectra recorded by the space-borne ACE-FTS Earth observation mission (Hughes et al., ACE infrared spectral atlases of the Earth's atmosphere, JQSRT 2014) and combine these spectra to the effective height of the atmosphere. These data are compared to spectra modeled with an atmospheric radiative transfer line-by-line infrared code to study the impact of individual molecules, spectral resolution, the choice of auxiliary data, and numerical approximations. Moreover, the study serves as a validation of our infrared radiative transfer code. The largest impact is due to water, carbon dioxide, ozone, methane, nitrous oxide, nitrogen, nitric acid, oxygen, and some chlorofluorocarbons (CFC11 and CFC12). The effect of further molecules considered in the modeling is either marginal or absent. The best matching model has a mean residuum of 0.4 km and a maximum difference of 2 km to the measured effective height. For a quantitative estimate of visibility and detectability we consider the maximum change of the residual spectrum, the relative change of the residual norm, the additional transit depth, and signal-to-noise ratios for a JWST setup. In conclusion, our study provides a list of molecules that are relevant for modeling transmission spectra of Earth-like exoplanets and discusses the feasibility of retrieval.

[65] arXiv:1803.05168v1 [pdf, vox]

A 1.6:1 Bandwidth Two-Layer Antireflection Structure for Silicon Matched to the 190-310 GHz Atmospheric Window

Fabien Defrance, Cecile Jung-Kubiak, Jack Sayers, Jake Connors, Clare deYoung, Matthew I. Hollister, Hiroshige Yoshida, Goutam Chattopadhyay, Sunil R. Golwala, Simon J. E. Radford
Submitted Wednesday 14 March 2018 @ 09:06:30 GMT

Although high-resistivity, low-loss silicon is an excellent material for THz transmission optics, its high refractive index necessitates antireflection treatment. We fabricated a wide-bandwidth, two-layer antireflection treatment by cutting subwavelength structures into the silicon surface using multi-depth deep reactive ion etching (DRIE). A wafer with this treatment on both sides has <-20 dB (<1%) reflectance over 190-310 GHz. We also demonstrated that bonding wafers introduces no reflection features above the -20 dB level, reproducing previous work. Together these developments immediately enable construction of wide-bandwidth silicon vacuum windows and represent two important steps toward gradient-index silicon optics with integral broadband antireflection treatment.

[66] arXiv:1803.05154v1 [pdf, vox]

The Origin of the Milky Way's Halo Age Distribution

Daniela Carollo, Patricia B. Tissera, Timothy C. Beers, Dmitrii Gudin, Brad K. Gibson, Ken C. Freeman, Antonela Monachesi
Submitted Wednesday 14 March 2018 @ 07:36:29 GMT
5 pages, 3 figures, submitted to ApJ Letter

We present an analysis of the radial age gradients for the stellar halos of five Milky Way mass-sized systems simulated as part of the Aquarius Project. The halos show a diversity of age trends, reflecting their different assembly histories. Four of the simulated halos possess clear negative age gradients, ranging from approximately -7 to -19 Myr/kpc , shallower than those determined by recent observational studies of the Milky Way's stellar halo. However, when restricting the analysis to the accreted component alone, all of the stellar halos exhibit a steeper negative age gradient with values ranging from $-$8 to $-$32~Myr/kpc, closer to those observed in the Galaxy. Two of the accretion-dominated simulated halos show a large concentration of old stars in the center, in agreement with the Ancient Chronographic Sphere reported observationally. The stellar halo that best reproduces the current observed characteristics of the age distributions of the Galaxy is that formed principally by the accretion of small satellite galaxies. Our findings suggest that the hierarchical clustering scenario can reproduce the MW's halo age distribution if the stellar halo was assembled from accretion and disruption of satellite galaxies with dynamical masses less than ~10^9.5M_sun, and a minimal in situ contribution.

[67] arXiv:1803.05124v1 [pdf, vox]

Galactic or extragalactic chemical tagging for NGC3201? Discovery of an anomalous CN-CH relation

Bruno Dias, Ignacio Araya, João Paulo Nogueira-Cavalcante, Leila Saker, Ahmed Shokry
Submitted Wednesday 14 March 2018 @ 03:42:10 GMT
15 pages, 17 figures, accepted for publication at Astronomy & Astrophysics

(ABRIDGED) The origin of the globular cluster (GC) NGC3201 is under debate. Its retrograde orbit points to an extragalactic origin, but no further chemical evidence supports this idea. Light-element chemical abundances are useful to tag GCs and can be used to shed light on this discussion. We aim to derive CN and CH band strengths for red giant stars in NGC3201 and compare these with photometric indices and high-resolution spectroscopy and discuss in the context of GC chemical tagging. We found three groups in the CN-CH distribution. A main sequence (S1), a secondary less-populated sequence (S2), and a group of peculiar (pec) CN-weak and CH-weak stars, one of which was previously known. The three groups seem to have different C+N+O and/or s-process element abundances, to be confirmed by high-resolution spectroscopy. These are typical characteristics of anomalous GCs. The CN distribution of NGC 3201 is quadrimodal, which is more common in anomalous clusters. However, NGC3201 does not belong to the trend of anomalous GCs in the mass-size relation. Three scenarios are postulated here: (i) if the sequence pec-S1-S2 has increasing C+N+O and s-process element abundances, NGC3201 would be the first anomalous GC outside of the mass-size relation; (ii) if the abundances are almost constant, NGC3201 would be the first non-anomalous GC with multiple CN-CH anti-correlation groups; or (iii) it would be the first anomalous GC without variations in C+N+O and s-process element abundances. In all cases, the definition of anomalous clusters and the scenario in which they have an extragalactic origin must be revised.

[68] arXiv:1803.04854v2 [pdf, vox]

M101: Spectral Observations of HII Regions and Their Physical Properties

Ning Hu, Enci Wang, Zesen Lin, Xu Kong, Fuzhen Cheng, Zou Fan, Guanwen Fang, Lin Lin, Yewei Mao, Jing Wang, Xu Zhou, Zhiming Zhou, Yinan Zhu, Hu Zou
Submitted Wednesday 14 March 2018 @ 02:43:27 GMT
7 figures, 23 pages, accepted for publication in ApJ

By using the Hectospec 6.5 m Multiple Mirror Telescope (MMT) and the 2.16 m telescope of National Astronomical Observatories, Chinese Academy of Sciences (NAOC), we obtained 188 high signal-to-noise ratio (S/N) spectra of HII regions in the nearby galaxy M101, which are the largest spectroscopic sample of HII regions for this galaxy so far. These spectra cover a wide range of regions on M101, which enables us to analyze two dimensional distributions of its physical properties. The physical parameters are derived from emission lines or stellar continuum, including stellar population age, electron temperature, oxygen abundance and etc. The oxygen abundances are derived using two empirical methods based on O3N2 and R$_{23}$ indicators, as well as the direct Te method when OIII$\lambda4363$ is available. By applying the harmonic decomposition analysis to the velocity field, we obtained line-of-sight rotation velocity of 71 km s$^{-1}$ and a position angle of 36 degree. The stellar age profile shows an old stellar population in galaxy center and a relative young stellar population in outer regions, suggesting an old bulge and a young disk. Oxygen abundance profile exhibits a clear break at $\sim$18 kpc, with a gradient of $-$0.0364 dex kpc$^{-1}$ in the inner region and $-$0.00686 dex kpc$^{-1}$ in the outer region. Our results agree with the "inside-out" disk growth scenario of M101.

[69] arXiv:1803.05095v1 [pdf, vox]

OGLE-2017-BLG-1522: A giant planet around a brown dwarf located in the Galactic bulge

Y. K. Jung, A. Udalski, A. Gould, Y. -H. Ryu, J. C. Yee, C. Han, M. D. Albrow, C. -U. Lee, S. -L. Kim, K. -H. Hwang, S. -J. Chung, I. -G. Shin, W. Zhu, S. -M. Cha, D. -J. Kim, Y. Lee, B. -G. Park, D. -J. Lee, H. -W. Kim, R. W. Pogge, M. K. Szymański, P. Mróz, R. Poleski, J. Skowron, P. Pietrukowicz, I. Soszyński, S. Kozłowski, K. Ulaczyk, M. Pawlak, K. Rybicki
Submitted Wednesday 14 March 2018 @ 01:36:29 GMT
20 pages, 6 figures

We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of $t_{\rm E} \sim 7.5$ days. The Einstein radius is unusually small, $\theta_{\rm E} = 0.065\,$mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses $(M_{\rm host}, M_{\rm planet})=(46_{-25}^{​+79}, 0.75_{-0.40}^{+1.26}​)~M_{\rm J}$ and source-lens distance $D_{\rm LS} = 0.99_{-0.54}^{+0.91}​~{\rm kpc}$, implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion $\mu = 3.2 \pm 0.5~{\rm mas}~{\rm yr^{-1}}$. The projected companion-host separation is $0.59_{-0.11}^{+0.12​}~{\rm AU}$, indicating that the planet is placed beyond the snow line of the host, i.e., $a_{sl} \sim 0.12~{\rm AU}$. Planet formation scenarios combined with the small companion-host mass ratio $q \sim 0.016$ and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown dwarf host.

[70] arXiv:1803.05089v1 [pdf, vox]

Energy Dissipation in the Upper Atmospheres of Trappist-1 Planets

O. Cohen, A. Glocer, C. Garraffo, J. D. Drake, J. M. Bell
Submitted Wednesday 14 March 2018 @ 00:57:42 GMT
6 pages, 1 table, 2 figures, accepted to ApJ Letters

We present a method to quantify the upper-limit of the energy transmitted from the intense stellar wind to the upper atmospheres of three of the Trappist-1 planets (e, f, and g). We use a formalism that treats the system as two electromagnetic regions, where the efficiency of the energy transmission between one region (the stellar wind at the planetary orbits) to the other (the planetary ionospheres) depends on the relation between the conductances and impedances of the two regions. Since the energy flux of the stellar wind is very high at these planetary orbits, we find that for the case of high transmission efficiency (when the conductances and impedances are close in magnitude), the energy dissipation in the upper planetary atmospheres is also very large. On average, the Ohmic energy can reach $0.5-1~W/m^2$, about 1\% of the stellar irradiance and 5-15 times the EUV irradiance. Here, using constant values for the ionospheric conductance, we demonstrate that the stellar wind energy could potentially drive large atmospheric heating in terrestrial planets, as well as in hot jupiters. More detailed calculations are needed to assess the ionospheric conductance and to determine more accurately the amount of heating the stellar wind can drive in close-orbit planets.

[71] arXiv:1803.05088v1 [pdf, vox]

Observation of an Unusual Upward-going Cosmic-ray-like Event in the Third Flight of ANITA

P. W. Gorham, B. Rotter, P. Allison, O. Banerjee, L. Batten, J. J. Beatty, K. Bechtol, K. Belov, D. Z. Besson, W. R. Binns, V. Bugaev, P. Cao, C. C. Chen, C. H. Chen, P. Chen, J. M. Clem, A. Connolly, L. Cremonesi, B. Dailey, C. Deaconu, P. F. Dowkontt, B. D. Fox, J. W. H. Gordon, C. Hast, B. Hill, K. Hughes, J. J. Huang, R. Hupe, M. H. Israel, A. Javaid, J. Lam, K. M. Liewer, S. Y. Lin, T. C. Liu, A. Ludwig, L. Macchiarulo, S. Matsuno, C. Miki, K. Mulrey, J. Nam, C. J. Naudet, R. J. Nichol, A. Novikov, E. Oberla, M. Olmedo, R. Prechelt, S. Prohira, B. F. Rauch, J. M. Roberts, A. Romero-Wolf, J. W. Russell, D. Saltzberg, D. Seckel, H. Schoorlemmer, J. Shiao, S. Stafford, J. Stockham, M. Stockham, B. Strutt, G. S. Varner, A. G. Vieregg, S. H. Wang, S. A. Wissel
Submitted Wednesday 14 March 2018 @ 00:57:09 GMT
5 pages, 4 figures. Supplemental material available from corresponding author by request

We report on an upward traveling, radio-detected cosmic-ray-like impulsive event with characteristics closely matching an extensive air shower. This event, observed in the third flight of the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload, is consistent with a similar event reported in a previous flight. These events may be produced by the atmospheric decay of an upward-propagating $\tau$-lepton produced by a $\nu_{\tau}$ interaction, although their relatively steep arrival angles create tension with the standard model (SM) neutrino cross section. Each of the two events have $a~posteriori$ background estimates of $\lesssim 10^{-2}$ events. If these are generated by $\tau$-lepton decay, then either the charged-current $\nu_{\tau}$ cross section is suppressed at EeV energies, or the events arise at moments when the peak flux of a transient neutrino source was much larger than the typical expected cosmogenic background neutrinos.

Submitted Tue, 13 Mar 2018

[72] arXiv:1803.05076v1 [pdf, vox]

Galaxy And Mass Assembly (GAMA): impact of the group environment on galaxy star formation

S. Barsanti, M. S. Owers, S. Brough, L. J. M. Davies, S. P. Driver, M. L. P. Gunawardhana, B. W. Holwerda, J. Liske, J. Loveday, K. A. Pimbblet, A. S. G. Robotham, E. N. Taylor
Submitted Tuesday 13 March 2018 @ 23:49:38 GMT
23 pages, 31 figures

We explore how the group environment may affect the evolution of star-forming galaxies. We select 1197 Galaxy And Mass Assembly (GAMA) groups at $0.05\leq z \leq 0.2$ and analyze the projected phase space (PPS) diagram, i.e. the galaxy velocity as a function of projected group-centric radius, as a local environmental metric in the low-mass halo regime $10^{12}\leq (M_{200}/M_{\odot})< 10^{14}$. We study the properties of star-forming group galaxies, exploring the correlation of star formation rate (SFR) with radial distance and stellar mass. We find that the fraction of star-forming group members is higher in the PPS regions dominated by recently accreted galaxies, whereas passive galaxies dominate the virialized regions. We observe a small decline in specific SFR of star-forming galaxies towards the group center by a factor $\sim 1.2$ with respect to field galaxies. Similar to cluster studies, we conclude for low-mass halos that star-forming group galaxies represent an infalling population from the field to the halo and show suppressed star formation.

[73] arXiv:1803.05072v1 [pdf, vox]

On the shape of the gamma-ray spectrum around the "$π^0$-bump"

Rui-zhi Yang, Ervin Kafexhiu, Felix Aharonian
Submitted Tuesday 13 March 2018 @ 23:22:59 GMT
submitted to A&A

The "pion-decay" bump is a distinct signature of the differential energy spectrum of $\gamma$-rays between 100 MeV and 1 GeV produced in hadronic interactions of accelerated particles (cosmic rays) with the ambient gas. We use the recent parametrisations of relevant cross-sections to study the formation of the "pion-decay" bump. The $\gamma$-ray spectrum below the maximum of this spectral feature can be distorted because of contributions of additional radiation components, in particular, due to the bremsstrahlung of secondary electrons and positrons, the products of decays of $\pi^\pm$-mesons, accompanying the $\pi^0$-production. At energies below 100 MeV, a non-negligible fraction of $\gamma$-ray flux could originate from interactions of sub-relativistic heavy ions. We study the impact of these radiation channels on the formation of the overall $\gamma$-ray spectrum based on a time-dependent treatment of evolution of energy distributions of the primary and secondary particles in the $\gamma$-ray production region.

[74] arXiv:1803.05065v1 [pdf, vox]

Surface and Temporal Biosignatures

Edward W. Schwieterman
Submitted Tuesday 13 March 2018 @ 22:15:56 GMT
26 pages, 9 figures, review to appear in Handbook of Exoplanets

Recent discoveries of potentially habitable exoplanets have ignited the prospect of spectroscopic investigations of exoplanet surfaces and atmospheres for signs of life. This chapter provides an overview of potential surface and temporal exoplanet biosignatures, reviewing Earth analogues and proposed applications based on observations and models. The vegetation red-edge (VRE) remains the most well-studied surface biosignature. Extensions of the VRE, spectral "edges" produced in part by photosynthetic or nonphotosynthetic pigments, may likewise present potential evidence of life. Polarization signatures have the capacity to discriminate between biotic and abiotic "edge" features in the face of false positives from band-gap generating material. Temporal biosignatures -- modulations in measurable quantities such as gas abundances (e.g., CO2), surface features, or emission of light (e.g., fluorescence, bioluminescence) that can be directly linked to the actions of a biosphere -- are in general less well studied than surface or gaseous biosignatures. However, remote observations of Earth's biosphere nonetheless provide proofs of concept for these techniques and are reviewed here. Surface and temporal biosignatures provide complementary information to gaseous biosignatures, and while likely more challenging to observe, would contribute information inaccessible from study of the time-averaged atmospheric composition alone.

[75] arXiv:1803.05056v1 [pdf, vox]

Three small planets transiting the bright young field star EPIC 249622103

Trevor J. David, Ian J. M. Crossfield, Björn Benneke, Erik A. Petigura, Erica J. Gonzales, Joshua E. Schlieder, Liang Yu, Howard T. Isaacson, Andrew W. Howard, David R. Ciardi, Eric E. Mamajek, Lynne A. Hillenbrand, Ann Marie Cody, Adric Riedel, Hans Martin Schwengeler, Christopher Tanner, Martin Ende
Submitted Tuesday 13 March 2018 @ 21:35:03 GMT
Submitted to AAS journals. 13 pages, 3 figures, 2 tables

We report the detection of three small transiting planets around the young K3 dwarf EPIC 249622103 (2MASS J15215519-2013539) from observations during Campaign 15 of the K2 mission. The star is relatively nearby ($d$ = 69 pc) and bright ($V$ = 10.7 mag, $K_s$ = 8.4 mag), making the planetary system an attractive target for radial velocity follow-up and atmospheric characterization with the James Webb Space Telescope. The inner two planets are hot super-Earths ($R_b$ = 1.40 $\pm$ 0.06 R$_\oplus$, $R_c$ = 1.34 $\pm$ 0.08 R$_\oplus$), while the outer planet is a warm sub-Neptune ($R_d$ = 2.6 $\pm$ 0.1 R$_\oplus$). We estimate the stellar age to be 360$^{+490}_{-140}$ Myr based on rotation, activity, and kinematic indicators. The EPIC 249622103 system is particularly interesting given recent evidence for inflated radii in planets around similarly-aged stars, a trend potentially related to photo-evaporation, core-cooling, or both mechanisms.

[76] arXiv:1803.05055v1 [pdf, vox]

Magnetic Fields Recorded by Chondrules Formed in Nebular Shocks

Chuhong Mai, Steven J. Desch, Aaron C. Boley, Benjamin P. Weiss
Submitted Tuesday 13 March 2018 @ 21:27:03 GMT
17 pages, 11 figures, accepted for publication in ApJ

Recent laboratory efforts (Fu et al., 2014) have constrained the remanent magnetizations of chondrules and the magnetic field strengths at which the chondrules were exposed to as they cooled below their Curie points. An outstanding question is whether the inferred paleofields represent the background magnetic field of the solar nebula or were unique to the chondrule-forming environment. We investigate the amplification of the magnetic field above background values for two proposed chondrule formation mechanisms, large-scale nebular shocks and planetary bow shocks. Behind large-scale shocks, the magnetic field parallel to the shock front is amplified by factors $\sim 10-30$, regardless of the magnetic diffusivity. Therefore, chondrules melted in these shocks probably recorded an amplified magnetic field. Behind planetary bow shocks, the field amplification is sensitive to the magnetic diffusivity. We compute the gas properties behind a bow shock around a 3000 km-radius planetary embryo, with and without atmospheres, using hydrodynamics models. We calculate the ionization state of the hot, shocked gas, including thermionic emission from dust, and thermal ionization of gas-phase potassium atoms, and the magnetic diffusivity due to Ohmic dissipation and ambipolar diffusion. We find that the diffusivity is sufficiently large that magnetic fields have already relaxed to background values in the shock downstream where chondrules acquire magnetizations, and that these locations are sufficiently far from the planetary embryos that chondrules should not have recorded a significant putative dynamo field generated on these bodies. We conclude that, if melted in planetary bow shocks, chondrules probably recorded the background nebular field.

[77] arXiv:1803.05041v1 [pdf, vox]

Metal-Poor Type II Cepheids with Periods Less Than Three Days

V. Kovtyukh, G. Wallerstein, I. Yegorova, S. Andrievsky, S. Korotin, I. Saviane, S. Belik, C. E. Davis, E. M. Farrell
Submitted Tuesday 13 March 2018 @ 21:01:31 GMT

We have analysed 10 high resolution spectra of Type II Cepheids with periods less than 3 days. We find that they clearly separate into two groups: those with near or slightly below solar metallicities, and those with [Fe/H] between --1.5 and --2.0. While the former are usually called BL~Her stars, we suggest that the latter be called UY~Eri stars. The UY~Eri subclass appears to be similar to the short period variables in globular clusters of the Galactic Halo. Globular clusters with [Fe/H] $\textgreater$ --1.0 almost never have Type II Cepheids.

[78] arXiv:1803.05029v1 [pdf, vox]

Stellar Parameters and Radial Velocities of Hot Stars in the Carina Nebula

Richard J. Hanes, M. Virginia McSwain, Matthew S. Povich
Submitted Tuesday 13 March 2018 @ 20:09:34 GMT
Accepted to AAS Journals (29 pages, 6 figures)

The Carina Nebula is an active star forming region in the southern sky that is of particular interest due to the presence of a large number of massive stars in a wide array of evolutionary stages. Here we present the results of the spectroscopic analysis of 82 B-type stars and 33 O-type stars that were observed in 2013 and 2014. For 82 B-type stars without line blending, we fit model spectra from the Tlusty BSTAR2006 grid to the observed profiles of H{\gamma} and He {\lambda}{\lambda} 4026, 4388, and 4471 to measure the effective temperatures, surface gravities, and projected rotational velocities. We also measure the masses, ages, radii, bolometric luminosities, and distances of these stars. From the radial velocities measured in our sample, we find 31 single lined spectroscopic binary candidates. We find a high dispersion of radial velocities among our sample stars, and we argue that the Carina Nebula stellar population has not yet relaxed and become virialized.

[79] arXiv:1803.05023v1 [pdf, vox]

Project VeSElkA: results of abundance analysis for HD53929 and HD63975

Mamadou L. Ndiaye, Francis LeBlanc, Viktor Khalack
Submitted Tuesday 13 March 2018 @ 19:52:41 GMT
7 pages, 3 figures, accepted for publication in MNRAS

Project VeSElkA (Vertical Stratification of Element Abundances) has been initiated with the aim to detect and study the vertical stratification of element abundances in the atmosphere of chemically peculiar stars. Abundance stratification occurs in hydrodynamically stable stellar atmospheres due to the migration of the elements caused by atomic diffusion. Two HgMn stars, HD53929 and HD63975 were selected from the VeSElkA sample and analysed with the aim to detect some abundance peculiarities employing the ZEEMAN2 code. We present the results of abundance analysis of HD53929 and HD63975 observed recently with the spectropolarimeter ESPaDOnS at Canada-France-Hawaii Telescope. Evidence of phosphorus vertical stratification was detected in the atmosphere of these two stars. In both cases, phosphorus abundance increases strongly towards the superficial layers. The strong overabundance of Mn found in stellar atmosphere of both stars confirms that they are HgMn type stars.

[80] arXiv:1803.03892v2 [pdf, vox]

Toward Understanding the B[e] Phenomenon. VII. AS 386, a single-lined binary with a candidate black hole component

S. A. Khokhlov, A. S. Miroshnichenko, S. V. Zharikov, N. Manset, A. A. Arkharov, N. Efimova, S. Klimanov, V M. Larionov, A. V. Kusakin, R. I. Kokumbaeva, Ch. T. Omarov, K. S. Kuratov, A. K. Kuratova, R. J. Rudy, E. A. Laag, K. B. Crawford, T. K. Swift, R. C. Puetter, R. B. Perry, S. D. Chojnowski, A. Agishev, D. B. Caton, R. L. Hawkins, A. B. Smith, D. E. Reichart, V. V. Kouprianov, J. B. Haislip
Submitted Tuesday 13 March 2018 @ 19:06:13 GMT
18 pages, 4 tables, 13 figures, Accepted for publication in ApJ

We report the results of spectroscopic and photometric observations of the emission-line object AS 386. For the first time, we found that it exhibits the B[e] phenomenon and fits the definition of an FS CMa type object. The optical spectrum shows the presence of a B-type star with the following properties: T_ eff = 11000+/-500 K, log L/L_sun = 3.7+/-0.3, a mass of 7+/-1 M_sun, and a distance D = 2.4+/-0.3 kpc from the Sun. We detected regular radial velocity variations of both absorption and emission lines with the following orbital parameters: P_orb = 131.27+/-0.09 days, semi-amplitude K_1 = 51.7+/-3.0 km/s, systemic radial velocity gamma = -31.8+/-2.6 km/s, and a mass function of f(m) = 1.9+/-0.3 M_sun. AS 386 exhibits irregular variations of the optical brightness (V=10.92+/-0.05 mag), while the near-IR brightness varies up to ~0.3 mag following the spectroscopic period. We explain this behavior by a variable illumination of the dusty disk inner rim by the B-type component. Doppler tomography based on the orbital variations of emission-line profiles shows that the material is distributed near the B-type component and in a circumbinary disk. We conclude that the system has undergone a strong mass transfer that created the circumstellar material and increased the B-type component mass. The absence of any traces of a secondary component, whose mass should be >= 7 M_sun, suggests that it is most likely a black hole.

[81] arXiv:1803.05009v1 [pdf, vox]

Tidal disruption of stars in a supermassive black hole binary system: the influence of orbital properties on fallback and accretion rates

Quentin Vigneron, Giuseppe Lodato, Alessio Guidarelli
Submitted Tuesday 13 March 2018 @ 19:01:24 GMT
12 pages, 7 figures, accepted in MNRAS. DOI: 10.1093/mnras/sty585

The disruption of a star by a supermassive black hole generates a sudden bright flare. Previous studies have focused on the disruption by single black holes, for which the fallback rate decays as~$\propto t^{-5/3}$. In this paper, we generalise the study to the case of a supermassive black hole binary (SMBHB), using both analytical estimates and hydrodynamical simulations, looking for specific observable signatures. The range of binary separation for which it is possible to distinguish between the disruption created by a single or a binary black hole concerns typically separations of order a few milliparsecs for a primary of mass $\sim 10^6M_{\odot}$. When the fallback rate is affected by the secondary, it undergoes two types interruptions, depending on the initial inclination $\theta$ of the orbit of the star relative to the plane of the SMBHB. For $\theta \lesssim 70^\circ$, periodic sharp interruptions occur and the time of first interruption depends on the distance of the secondary black hole with the debris. If $\theta \gtrsim 70^\circ$, a first smooth interruption occurs, but not always followed by a further recovery of the fallback rate. This implies that most of the TDEs around a SMBHB will undergo periodic sharp interruptions of their lightcurve.

[82] arXiv:1803.05007v1 [pdf, vox]

X-ray scaling relations from a complete sample of the richest maxBCG clusters

Chong Ge, Andrea Morandi, Ming Sun, Eduardo Rozo, Neelima Sehgal, Alexey Vikhlinin, William Forman, Christine Jones, Daisuke Nagai
Submitted Tuesday 13 March 2018 @ 19:00:05 GMT
26 pages, 11 figures, submitted to MNRAS

The galaxy cluster scaling relations are important for studying baryon physics, structure formation and cosmology. We use a complete sample of 38 richest maxBCG clusters to study the ICM-galaxy scaling relations based on X-ray and optical observations. The clusters are selected from the two largest bins of optical richness in the Planck stacking work with the maxBCG richness N200 > 78. We analyze their Chandra and XMM-Newton data to derive the X-ray properties of the ICM. While the expected cluster temperatures should be scattered around 5-10 keV from the optical richness, the observed range extends to temperatures as low as 1.5 keV. Meanwhile, they follow normal Lx-Tx and Lx-Yx relations, which suggests that they are normal X-ray clusters. Moreover, the observed average Yx is consistent with the expected Yx inferred from the Planck mean staking Ysz in the same two richest bins. However, the scatter of the Lx-N and Yx-N relations are also large and asymmetric with more outliers towards lower Lx or Yx. The mismatch between ICM-galaxy scaling relations can come from several factors, including miscentering, projection, contamination of low mass systems, mass bias and covariance bias. The mismatch is smaller when using a BCG-dominated subsample, with the outliers suffering from the projection problem. Our results suggest that results from blind stacking should be interpreted carefully. We also evaluate the fractions of relaxed and cool core (CC) clusters in our sample. Both are smaller than those from SZ or X-ray selected samples.

[83] arXiv:1803.05005v1 [pdf, vox]

Python: a Python package for VLT/MUSE data

Ismael Pessa, Nicolas Tejos, Cristobal Moya
Submitted Tuesday 13 March 2018 @ 18:58:29 GMT
Proceedings of Astronomical Data Analysis Software and Systems XXVII conference

This is a companion Focus Demonstration article to the PyMUSE python package, demonstrating its usage and utilities for VLT/MUSE data analysis, that include a wide range of options for spectra extractions, the creation of different types of images, compatibilities with some commonly used software for astronomical data analysis, among others. PyMUSE is an open-source software and can be found on Github for free use and distribution.

[84] arXiv:1803.05000v1 [pdf, vox]

Stellar obliquities and magnetic activities of Planet-Hosting Stars and Eclipsing Binaries based on Transit Chord Correlation

Fei Dai, Joshua N. Winn, Zachory Berta-Thompson, Roberto Sanchis-Ojeda, Simon Albrecht
Submitted Tuesday 13 March 2018 @ 18:42:52 GMT
Accepted to AJ

The light curve of an eclipsing system shows anomalies whenever the eclipsing body passes in front of active regions on the eclipsed star. In some cases, the pattern of anomalies can be used to determine the obliquity $\Psi$ of the eclipsed star. Here we present a method for detecting and analyzing these patterns, based on a statistical test for correlations between the anomalies observed in a sequence of eclipses. Compared to previous methods, ours makes fewer assumptions and is easier to automate. We apply it to a sample of 64 stars with transiting planets and 24 eclipsing binaries for which precise space-based data are available, and for which there was either some indication of flux anomalies or a previously reported obliquity measurement. We were able to determine obliquities for ten stars with hot Jupiters. In particular we found $\Psi \lesssim$10$^\circ$ for Kepler-45, which is only the second M dwarf with a measured obliquity. The other 8 cases are G and K stars with low obliquities. Among the eclipsing binaries, we were able to determine obliquities in 8 cases, all of which are consistent with zero. Our results also reveal some common patterns of stellar activity for magnetically active G and K stars, including persistently active longitudes.

[85] arXiv:1803.04992v1 [pdf, vox]

SU(N) - symmetric dynamic aether: General formalism and a hypothesis on spontaneous color polarization

Alexander B. Balakin, Alexey V. Andreyanov
Submitted Tuesday 13 March 2018 @ 18:09:36 GMT
23 pages, Invited paper for the Journal "Space, Time and Fundamental Interactions"

The SU(N)-symmetric generalization of the model of the electromagnetically active dynamic aether is formulated. This generalization is based on the introduction of a Yang-Mills gauge field instead of the Maxwell field, and of a SU(N)-multiplet of vector fields instead of the standard single vector field. In the framework of the second order version of the effective field theory this generalization includes three constitutive tensors, which are the SU(N) extensions of the tensors appeared in the Einstein-Maxwell-aet​her theory; we reconstructed the full-format set of these constitutive tensors. The total self-consistent system of master equations for the gauge, vector and gravitational fields is obtained by the variation procedure. The general model of the SU(N)-symmetric dynamic aether is reduced to the extended Einstein-Yang-Mills-​aether model by the ansatz about spontaneous color polarization of the vector fields. In fact, this ansatz requires the vector fields, which form the SU(N) multiplet, to become parallel in the group (color) space due to a phase transition, and a new selected direction in the group space to appear, thus converting it into the anisotropic color space.

[86] arXiv:1803.04987v1 [pdf, vox]

Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering

Ryan A. Loomis, Karin I. Öberg, Sean M. Andrews, Catherine Walsh, Ian Czekala, Jane Huang, Katherine Rosenfeld
Submitted Tuesday 13 March 2018 @ 18:03:24 GMT
20 pages, 8 figures, accepted for publication in The Astronomical Journal

Modern radio interferometers enable observations of spectral lines with unprecedented spatial resolution and sensitivity. In spite of these technical advances, many lines of interest are still at best weakly detected and therefore necessitate detection and analysis techniques specialized for the low signal-to-noise ratio (SNR) regime. Matched filters can leverage knowledge of the source structure and kinematics to increase sensitivity of spectral line observations. Application of the filter in the native Fourier domain improves SNR while simultaneously avoiding the computational cost and ambiguities associated with imaging, making matched filtering a fast and robust method for weak spectral line detection. We demonstrate how an approximate matched filter can be constructed from a previously observed line or from a model of the source, and we show how this filter can be used to robustly infer a detection significance for weak spectral lines. When applied to ALMA Cycle 2 observations of CH3OH in the protoplanetary disk around TW Hya, the technique yields a ~53% SNR boost over aperture-based spectral extraction methods, and we show that an even higher boost will be achieved for observations at higher spatial resolution. A Python-based open-source implementation of this technique is available under the MIT license at​stroChem/VISIBLE.

[87] arXiv:1803.04986v1 [pdf, vox]

A Survey of CH3CN and HC3N in Protoplanetary Disks

Jennifer B. Bergner, Viviana G. Guzman, Karin I. Oberg, Ryan A. Loomis, Jamila Pegues
Submitted Tuesday 13 March 2018 @ 18:03:22 GMT

The organic content of protoplanetary disks sets the initial compositions of planets and comets, thereby influencing subsequent chemistry that is possible in nascent planetary systems. We present observations of the complex nitrile-bearing species CH3CN and HC3N towards the disks around the T Tauri stars AS 209, IM Lup, LkCa 15, and V4046 Sgr as well as the Herbig Ae stars MWC 480 and HD 163296. HC3N is detected towards all disks except IM Lup, and CH3CN is detected towards V4046 Sgr, MWC 480, and HD 163296. Rotational temperatures derived for disks with multiple detected lines range from 29-73K, indicating emission from the temperate molecular layer of the disk. V4046 Sgr and MWC 480 radial abundance profiles are constrained using a parametric model; the gas-phase CH3CN and HC3N abundances with respect to HCN are a few to tens of percent in the inner 100 AU of the disk, signifying a rich nitrile chemistry at planet- and comet-forming disk radii. We find consistent relative abundances of CH3CN, HC3N, and HCN between our disk sample, protostellar envelopes, and solar system comets; this is suggestive of a robust nitrile chemistry with similar outcomes under a wide range of physical conditions.

[88] arXiv:1803.04985v1 [pdf, vox]

The Transiting Exoplanet Community Early Release Science Program for JWST

Jacob L. Bean, Kevin B. Stevenson, Natalie M. Batalha, Zachory Berta-Thompson, Laura Kreidberg, Nicolas Crouzet, Björn Benneke, Michael R. Line, David K. Sing, Hannah R. Wakeford, Heather A. Knutson, Eliza M. -R. Kempton, Jean-Michel Désert, Ian Crossfield, Natasha E. Batalha, Julien de Wit, Vivien Parmentier, Joseph Harrington, Julianne I. Moses, Mercedes Lopez-Morales, Munazza K. Alam, Jasmina Blecic, Giovanni Bruno, Aarynn L. Carter, John W. Chapman, Leen Decin, Diana Dragomir, Thomas M. Evans, Jonathan J. Fortney, Jonathan D. Fraine, Peter Gao, Antonio García Muñoz, Neale P. Gibson, Jayesh M. Goyal, Kevin Heng, Renyu Hu, Sarah Kendrew, Brian M. Kilpatrick, Jessica Krick, Pierre-Olivier Lagage, Monika Lendl, Tom Louden, Nikku Madhusudhan, Avi M. Mandell, Megan Mansfield, Erin M. May, Giuseppe Morello, Caroline V. Morley, Nikolay Nikolov, Seth Redfield, Jessica E. Roberts, Everett Schlawin, Jessica J. Spake, Kamen O. Todorov, Angelos Tsiaras, Olivia Venot, William C. Waalkes, Peter J. Wheatley, Robert T. Zellem, Daniel Angerhausen, David Barrado, Ludmila Carone, Sarah L. Casewell, Patricio E. Cubillos, Mario Damiano, Miguel de Val-Borro, Benjamin Drummond, Billy Edwards, Michael Endl, Nestor Espinoza, Kevin France, John E. Gizis, Thomas P. Greene, Thomas K. Henning, Yucian Hong, James G. Ingalls, Nicolas Iro, Patrick G. J. Irwin, Tiffany Kataria, Fred Lahuis, Jérémy Leconte, Jorge Lillo-Box, Stefan Lines, Luigi Mancini, Franck Marchis, Nathan Mayne, Enric Palle, Gaël Roudier, Evgenya L. Shkolnik, John Southworth, Johanna Teske, Giovanna Tinetti, Pascal Tremblin, Gregory S. Tucker, Roy vanBoekel, Ingo P. Waldmann, Ian C. Weaver, Tiziano Zingales
Submitted Tuesday 13 March 2018 @ 18:01:33 GMT
submitted to PASP

The James Webb Space Telescope (JWST) presents the opportunity to transform our understanding of planets and the origins of life by revealing the atmospheric compositions, structures, and dynamics of transiting exoplanets in unprecedented detail. However, the high-precision, time-series observations required for such investigations have unique technical challenges, and prior experience with other facilities indicates that there will be a steep learning curve when JWST becomes operational. In this paper we describe the science objectives and detailed plans of the Transiting Exoplanet Community Early Release Science (ERS) Program, which is a recently approved program for JWST observations early in Cycle 1. The goal of this project, for which the obtained data will have no exclusive access period, is to accelerate the acquisition and diffusion of technical expertise for transiting exoplanet observations with JWST, while also providing a compelling set of representative datasets that will enable immediate scientific breakthroughs. The Transiting Exoplanet Community ERS Program will exercise the time-series modes of all four JWST instruments that have been identified as the consensus highest priorities, observe the full suite of transiting planet characterization geometries (transits, eclipses, and phase curves), and target planets with host stars that span an illustrative range of brightnesses. The observations in this program were defined through an inclusive and transparent process that had participation from JWST instrument experts and international leaders in transiting exoplanet studies. Community engagement in the project will be centered on a two-phase Data Challenge that culminates with the delivery of planetary spectra, time-series instrument performance reports, and open-source data analysis toolkits in time to inform the agenda for Cycle 2 of the JWST mission.

[89] arXiv:1803.04983v1 [pdf, vox]

Ultra Long Gamma-Ray Bursts from the collapse of Blue Super Giant stars: an end-to-end simulation

Rosalba Perna, Davide Lazzati, Matteo Cantiello
Submitted Tuesday 13 March 2018 @ 18:00:18 GMT
7 pages, 6 figures, submitted to ApJ

Ultra-long gamma ray bursts (ULGRBs) are a distinct class of GRBs characterized by durations of several thousands of seconds, about two orders of magnitude longer than those of standard long GRBs (LGRBs). The driving engine of these events has not been uncovered yet, and ideas range from magnetars, to tidal disruption events, to extended massive stars, such as blue super giants (BSG). BSGs, a possible endpoint of stellar evolution, are attractive for the relatively long free-fall times of their envelopes, allowing accretion to power a long-lasting central engine. At the same time, their large radial extension poses a challenge to the emergence of a jet. Here we perform an end-to-end simulation aimed at assessing the viability of BSGs as ULGRB progenitors. The evolution to core collapse of a BSG star model is calculated with the MESA code. We then compute the accretion rate for the fraction of envelope material with enough angular momentum to circularize and form an accretion disk, and input the corresponding power into a jet which we evolve through the star envelope with the FLASH code. Our simulation shows that the jet can emerge, and the resulting light curves resemble those observed in ULGRBs, with durations $T_{90}$ ranging from $\approx$4000~s to $\approx10^4$ s depending on the viewing angle.

[90] arXiv:1803.04982v1 [pdf, vox]

Identifying Universality in Warm Inflation

Arjun Berera, Joel Mabillard, Mauro Pieroni, Rudnei O. Ramos
Submitted Tuesday 13 March 2018 @ 18:00:16 GMT
20 pages, 5 figures, 1 appendix

Ideas borrowed from renormalization group are applied to warm inflation to characterize the inflationary epoch in terms of flows away from the de Sitter regime. In this framework different models of inflation fall into universality classes. Furthermore, for warm inflation this approach also helps to characterise when inflation can smoothly end into the radiation dominated regime. Warm inflation has a second functional dependence compared to cold inflation due to dissipation, yet despite this feature, it is shown that the universality classes defined for cold inflation can be consistently extended to warm inflation.

[91] arXiv:1803.04981v1 [pdf, vox]

Unveiling the dynamical state of massive clusters through the ICL fraction

Y. Jiménez-Teja, R. Dupke, N. Benítez, A. M. Koekemoer, A. Zitrin, K. Umetsu, B. L. Ziegler, B. L. Frye, H. Ford, R. J. Bouwens, L. D. Bradley, T. Broadhurst, D. Coe, M. Donahue, G. J. Graves, C. Grillo, L. Infante, S. Jouvel, D. D. Kelson, O. Lahav, R. Lazkoz, D. Lemze, D. Maoz, E. Medezinski, P. Melchior, M. Meneghetti, A. Mercurio, J. Merten, A. Molino, L. A. Moustakas, M. Nonino, S. Ogaz, A. G. Riess, P. Rosati, J. Sayers, S. Seitz, W. Zheng
Submitted Tuesday 13 March 2018 @ 18:00:08 GMT
25 pages, 13 figures, 2 tables. Accepted for publication in ApJ

We have selected a sample of eleven massive clusters of galaxies observed by the Hubble Space Telescope in order to study the impact of the dynamical state on the IntraCluster Light (ICL) fraction, the ratio of total integrated ICL to the total galaxy member light. With the exception of the Bullet cluster, the sample is drawn from the Cluster Lensing and Supernova Survey and the Frontier Fields program, containing five relaxed and six merging clusters. The ICL fraction is calculated in three optical filters using the CHEFs IntraCluster Light Estimator, a robust and accurate algorithm free of a priori assumptions. We find that the ICL fraction in the three bands is, on average, higher for the merging clusters, ranging between $\sim7-23\%$, compared with the $\sim 2-11\%$ found for the relaxed systems. We observe a nearly constant value (within the error bars) in the ICL fraction of the regular clusters at the three wavelengths considered, which would indicate that the colors of the ICL and the cluster galaxies are, on average, coincident and, thus, their stellar populations. However, we find a higher ICL fraction in the F606W filter for the merging clusters, consistent with an excess of lower-metallicity/yo​unger stars in the ICL, which could have migrated violently from the outskirts of the infalling galaxies during the merger event.

[92] arXiv:1803.04979v1 [pdf, vox]

Phoebe: a surface dominated by water

Wesley C. Fraser, Michael E. Brown
Submitted Tuesday 13 March 2018 @ 18:00:06 GMT
16 pages, 8 figures, submitted to the Astrophysical Journal

The Saturnian irregular satellite, Phoebe, can be broadly described as a water-rich rock. This object, which presumably originated from the same primordial population shared by the dynamically excited Kuiper Belt Objects, has received high resolution spectral imaging during the Cassini flyby. We present a new analysis of the Visual Infrared Mapping Spectrometer observations of Phoebe, which critically, includes a geometry correction routine that enables pixel-by-pixel mapping of visible and infrared spectral cubes directly onto the Phoebe shape model, even when an image exhibits significant trailing errors. The result of our re-analysis is a successful match of 40 images, producing spectral maps covering the majority of Phoebe's surface, roughly a 3rd of which is imaged by high resolution observations (<22 km per pixel resolution). There is no spot on Phoebe's surface that is absent of water absorption. The regions richest in water are clearly associated with the Jason and South Pole impact basins. We find Phoebe exhibits only three spectral types, and a water-ice concentration that correlates with physical depth and visible albedo. The water-rich and water-poor regions exhibit significantly different crater size frequency distributions, and different large crater morphologies. We propose that Phoebe once had a water-poor surface whose water-ice concentration was enhanced by basin forming impacts which exposed richer subsurface layers. Finally, we demonstrate that the range of Phoebe's water-ice absorption spans the same range exhibited by dynamically excited Kuiper Belt Objects. The common water-ice absorption depths and primordial origins, and the association of Phoebe's water-rich regions with its impact basins, suggests the plausible idea that Kuiper Belt Objects also originated with water-poor surfaces that were enhanced through stochastic collisional modification.

[93] arXiv:1803.04971v1 [pdf, vox]

Forward Modeling of the Kepler Stellar Rotation Period Distribution: Interpreting Periods from Mixed and Biased Stellar Populations

Jennifer L. van Saders, Marc H. Pinsonneault, Mauro Barbieri
Submitted Tuesday 13 March 2018 @ 18:00:00 GMT
16 pages, 13 figures. Submitted to AAS Journals: Comments are welcome

Stellar surface rotation carries information about stellar parameters---particu​larly ages---and thus the large rotational datasets extracted from Kepler timeseries represent powerful probes of stellar populations. In this article, we address the challenge of interpreting such datasets with a forward-modeling exercise. We combine theoretical models of stellar rotation, a stellar population model for the galaxy, and prescriptions for observational bias and confusion to predict the rotation distribution in the Kepler field under standard "vanilla" assumptions. We arrive at two central conclusions: first, that standard braking models fail to reproduce the observed distribution at long periods, and second, that the interpretation of the period distribution is complicated by mixtures of unevolved and evolved stars and observational uncertainties. By assuming that the amplitude and thus detectability of rotational signatures is tied to the Rossby number, we show that the observed period distribution contains an apparent "Rossby edge" at $\textrm{Ro}_{thresh​} = 2.08$, above which long-period, high-Rossby number stars are either absent or undetected. This $\textrm{Ro}_{thresh​}$ is comparable to the Rossby number at which van Saders et al. (2016) observed the onset of weakened magnetic braking, and suggests either that this modified braking is in operation in the full Kepler population, or that stars undergo a transition in spottedness and activity at a very similar Rossby number. We discuss the observations necessary to disentangle these competing scenarios. (abridged)

[94] arXiv:1803.04972v1 [pdf, vox]

Revisiting the Cooling Flow Problem in Galaxies, Groups, and Clusters of Galaxies

M. McDonald, M. Gaspari, B. R. McNamara, G. R. Tremblay
Submitted Tuesday 13 March 2018 @ 18:00:00 GMT
16 pages, 10 figures, 6 tables. Submitted to ApJ. Comments welcome!

We present a study of 107 galaxies, groups, and clusters spanning ~3 orders of magnitude in mass, ~5 orders of magnitude in central galaxy star formation rate (SFR), ~4 orders of magnitude in the classical cooling rate (dM/dt) of the intracluster medium (ICM), and ~5 orders of magnitude in the central black hole accretion rate. For each system in this sample, we measure dM/dt using archival Chandra X-ray data and acquire the SFR and systematic uncertainty in the SFR by combining over 330 estimates from dozens of literature sources. With these data, we estimate the efficiency with which the ICM cools and forms stars, finding e_cool = SFR/(dM/dt) = 1.4 +/- 0.4% for systems with dM/dt > 30 Msun/yr. For these systems, we measure a slope in the SFR-dM/dt relation greater than unity, suggesting that the systems with the strongest cool cores are also cooling more efficiently. We propose that this may be related to, on average, higher black hole accretion rates in the strongest cool cores, which could influence the total amount (saturating near the Eddington rate) and dominant mode (mechanical vs radiative) of feedback. For systems with dM/dt < 30 Msun/yr, we find that the SFR and dM/dt are uncorrelated, and show that this is consistent with star formation being fueled at a low (but dominant) level by recycled ISM gas in these systems. We find an intrinsic log-normal scatter in SFR at fixed dM/dt of 0.52 +/- 0.06 dex, suggesting that cooling is tightly self-regulated over very long timescales, but can vary dramatically on short timescales. There is weak evidence that this scatter may be related to the feedback mechanism, with the scatter being minimized (~0.4 dex) in systems for which the mechanical feedback power is within a factor of two of the cooling luminosity.

[95] arXiv:1803.04974v1 [pdf, vox]

The Hubble Catalog of Variables (HCV)

K. V. Sokolovsky, A. Z. Bonanos, P. Gavras, M. Yang, D. Hatzidimitriou, M. I. Moretti, A. Karampelas, I. Bellas-Velidis, Z. Spetsieri, E. Pouliasis, I. Georgantopoulos, V. Charmandaris, K. Tsinganos, N. Laskaris, G. Kakaletris, A. Nota, D. Lennon, C. Arviset, B. C. Whitmore, T. Budavari, R. Downes, S. Lubow, A. Rest, L. Strolger, R. White
Submitted Tuesday 13 March 2018 @ 18:00:00 GMT
4 pages, 1 figure, proceedings of the IAU Symposium 339 Southern Horizons in Time-Domain Astronomy, 13-17 November 2017, Stellenbosch, South Africa

The Hubble Source Catalog (HSC) combines lists of sources detected on images obtained with the WFPC2, ACS and WFC3 instruments aboard the Hubble Space Telescope (HST) available in the Hubble Legacy Archive. The catalog contains time-domain information with about two million of its sources detected with the same instrument and filter in at least five HST visits. The Hubble Catalog of Variables (HCV) project aims to identify HSC sources showing significant brightness variations. A magnitude-dependent threshold in the median absolute deviation of photometric measurements (an outlier-resistant measure of lightcurve scatter) is adopted as the variability-detectio​n statistic. It is supplemented with a cut in $\chi_{\rm red}^2$ that removes sources with large photometric errors. A pre-processing procedure involving bad image identification, outlier rejection and computation of local magnitude zero-point corrections is applied to HSC lightcurves before computing the variability detection statistic. About 52000 HSC sources are identified as candidate variables, among which 7800 show variability in more than one filter. Visual inspection suggests that $\sim 70\%$ of the candidates detected in multiple filters are true variables while the remaining $\sim 30\%$ are sources with aperture photometry corrupted by blending, imaging artifacts or image processing anomalies. The candidate variables have AB magnitudes in the range 15-27$^{m}$ with the median 22$^{m}$. Among them are the stars in our own and nearby galaxies as well as active galactic nuclei.

[96] arXiv:1803.04975v1 [pdf, vox]

Lensing reconstruction from line intensity maps: the impact of gravitational nonlinearity

Simon Foreman, P. Daniel Meerburg, Alexander van Engelen, Joel Meyers
Submitted Tuesday 13 March 2018 @ 18:00:00 GMT
39+17 pages, 13 figures, 5 tables

We investigate the detection prospects for gravitational lensing of three-dimensional maps from upcoming line intensity surveys, focusing in particular on the impact of gravitational nonlinearities on standard quadratic lensing estimators. Using perturbation theory, we show that these nonlinearities can provide a significant contaminant to lensing reconstruction, even for observations at reionization-era redshifts. However, we show how this contamination can be mitigated with the use of a "bias-hardened" estimator. Along the way, we present an estimator for reconstructing long-wavelength density modes, in the spirit of the "tidal reconstruction" technique that has been proposed elsewhere, and discuss the dominant biases on this estimator. After applying bias-hardening, we find that a detection of the lensing potential power spectrum will still be challenging for the first phase of SKA-Low, CHIME, and HIRAX, with gravitational nonlinearities decreasing the signal to noise by a factor of a few compared to forecasts that ignore these effects. On the other hand, cross-correlations between lensing and galaxy clustering or cosmic shear from a large photometric survey look promising, provided that systematics can be sufficiently controlled. We reach similar conclusions for a single-dish survey inspired by CII measurements planned for CCAT-prime, suggesting that lensing is an interesting science target not just for 21cm surveys, but also for intensity maps of other lines.

[97] arXiv:1803.04962v1 [pdf, vox]

Galaxy And Mass Assembly (GAMA): Gas Fuelling of Spiral Galaxies in the Local Universe II. -- Direct Measurement of the Dependencies on Redshift and Host Halo Mass of Stellar Mass Growth in Central Disk Galaxies

M. W. Grootes, A. Dvornik, R. J. Laureijs, R. J. Tuffs, C. C. Popescu, A. S. G. Robotham, J. Liske, M. J. I. Brown, B. W. Holwerda, L. Wang
Submitted Tuesday 13 March 2018 @ 17:59:58 GMT
23 pages, 6 figures, 3 tables. Accepted for publication in MNRAS

We present a detailed analysis of the specific star formation rate -- stellar mass ($\mathrm{sSFR}-M_*$​) of $z\le 0.13$ disk central galaxies using a morphologically selected mass-complete sample ($M_* \ge 10^{9.5} M_{\odot}$). Considering samples of grouped and ungrouped galaxies, we find the $\mathrm{sSFR}-M_*$ relations of disk-dominated central galaxies to have no detectable dependence on host dark-matter halo (DMH) mass, even where weak-lensing measurements indicate a difference in halo mass of a factor $\gtrsim5$. We further detect a gradual evolution of the $\mathrm{sSFR}-M_*$ relation of non-grouped (field) central disk galaxies with redshift, even over a $\Delta z \approx 0.04$ ($\approx5\cdot10^{8​}\mathrm{yr}$) interval, while the scatter remains constant. This evolution is consistent with extrapolation of the "main-sequence-of-st​ar-forming-galaxies"​ from previous literature that uses larger redshift baselines and coarser sampling. Taken together, our results present new constraints on the paradigm under which the SFR of galaxies is determined by a self-regulated balance between gas inflows and outflows, and consumption of gas by star-formation in disks, with the inflow being determined by the product of the cosmological accretion rate and a fuelling-efficiency -- $\dot{M}_{\mathrm{b,​halo}}\zeta$. In particular, maintaining the paradigm requires $\dot{M}_{\mathrm{b,​halo}}\zeta$ to be independent of the mass $M_{\mathrm{halo}}$ of the host DMH. Furthermore, it requires the fuelling-efficiency $\zeta$ to have a strong redshift dependence ($\propto (1+z)^{2.7}$ for $M_*=10^{10.3} M_{\odot}$ over $z=0 - 0.13$), even though no morphological transformation to spheroids can be invoked to explain this in our disk-dominated sample. The physical mechanisms capable of giving rise to such dependencies of $\zeta$ on $M_{\mathrm{halo}}$ and $z$ for disks are unclear.

[98] arXiv:1803.04961v1 [pdf, vox]

Dark decay of the neutron

James M. Cline, Jonathan M. Cornell
Submitted Tuesday 13 March 2018 @ 17:59:09 GMT
8 pages, 2 figures

New decay channels for the neutron into dark matter plus other particles have been suggested for explaining a long-standing discrepancy between the neutron lifetime measured from trapped neutrons versus those decaying in flight. Many such scenarios are already ruled out by their effects on neutron stars, and the decay into dark matter plus photon has been experimentally excluded. Here we explore the decay into a dark Dirac fermion $\chi$ and a dark photon $A'$ which can be consistent with all constraints, if $\chi$ is a subdominant component of the dark matter. Neutron star constraints are evaded if the dark photon mass to coupling ratio is $m_{A'}/g' \lesssim (45-60)\,$MeV, depending upon the nuclear equation of state. $g'$ and the kinetic mixing between U(1)$'$ and electromagnetism are tightly constrained by direct and indirect detection, supernova constraints, and cosmological limits.

[99] arXiv:1803.03276v2 [pdf, vox]

The Fornax Cluster VLT Spectroscopic Survey II - Planetary Nebulae kinematics within 200 kpc of the cluster core

C. Spiniello, N. R. Napolitano, M. Arnaboldi, C. Tortora, L. Coccato, M. Capaccioli, O. Gerhard, E. Iodice, M. Spavone, M. Cantiello, R. Peletier, M. Paolillo, P. Schipani
Submitted Tuesday 13 March 2018 @ 17:31:45 GMT
13 pages, 8 figures, Accepted for publication in MNRAS, companion paper FVSS-I (Pota et al, 2018, submitted)

We present the largest and most spatially extended planetary nebulae (PNe) catalog ever obtained for the Fornax cluster. We measured velocities of 1452 PNe out to 200 kpc in the cluster core using a counter-dispersed slitless spectroscopic technique with data from FORS2 on the VLT. With such extended spatial coverage, we can study separately the stellar halos of some of the cluster main galaxies and the intracluster light. In this second paper of the Fornax Cluster VLT Spectroscopic Survey (FVSS), we identify and classify the emission-line sources, describe the method to select PNe and calculate their coordinates and velocities from the dispersed slitless images. From the PN 2D velocity map we identify stellar streams that are possibly tracing the gravitational interaction of NGC1399 with NGC1404 and NGC1387. We also present the velocity dispersion profile out to $\sim 200$ kpc radii, which shows signatures of a superposition of the bright central galaxy and the cluster potential, with the latter clearly dominating the regions outside R $\sim 1000$" ($\sim 100$ kpc).

[100] arXiv:1803.05345v1 [pdf, vox]

The ngVLA's Role in Exoplanet Science: Constraining Exo-Space Weather

Rachel A. Osten, Michael K. Crosley, Manuel Gudel, Adam F. Kowalski, Joe Lazio, Jeffrey Linsky, Eric Murphy, Stephen White
Submitted Tuesday 13 March 2018 @ 17:25:46 GMT
6 pages, white paper submitted to National Academy of Science Committee on Exoplanet Science Strategy. arXiv admin note: text overlap with arXiv:1711.05113

Radio observations are currently the only way to explore accelerated particles in cool stellar environments. We describe how a next generation VLA can contribute to the understanding of the stellar contribution to exo-space weather. This area holds both academic and popular interest, and is expected to grow in the next several decades.

[101] arXiv:1803.04919v1 [pdf, vox]

Implications of Neutron Star Mergers for Extraterrestrial Civilizations

Abraham Loeb
Submitted Tuesday 13 March 2018 @ 16:25:18 GMT
3 pages, no figures, published in Scientific American

The economy and fate of extraterrestrial civilizations should depend on the abundance of gold and uranium, made in neutron star mergers.

[102] arXiv:1803.04893v1 [pdf, vox]

A single population of red globular clusters around the massive compact galaxy NGC 1277

Michael A. Beasley, Ignacio Trujillo, Ryan Leaman, Mireia Montes
Submitted Tuesday 13 March 2018 @ 15:46:14 GMT
Published in Nature, 12 March 2018

Massive galaxies are thought to form in two phases: an initial, early collapse of gas and giant burst of central star formation, followed by the later accretion of material that builds up their stellar and dark matter haloes. The globular cluster systems of such galaxies are believed to form in a similar manner. The initial central burst forms metal-rich (red) clusters, while more metal-poor (blue) clusters are brought in by the later accretion of less massive satellites. This formation process is thought to lead the creation of the multimodal optical colour distributions seen in the globular cluster systems of massive galaxies. Here we report HST/ACS observations of the massive relic galaxy NGC 1277 and its globular clusters, a nearby unevolved example of a high redshift "red nugget". The g-z cluster colour distribution shows that the globular cluster system of the galaxy is unimodal and uniquely red. This is in strong contrast to normal galaxies of similar and larger stellar mass, whose cluster systems always exhibit (and are generally dominated by) blue clusters. We argue that the globular cluster system of NGC 1277 indicates that the galaxy has undergone little (if any) mass accretion after its initial collapse and use analytic merger trees to show that the total stellar mass accretion is likely less than ~ 10 %. These results confirm that NGC 1277 is a genuine relic galaxy and show that the blue, metal-poor globular clusters constitute an accreted population in present day massive galaxies.

[103] arXiv:1803.04891v1 [pdf, vox]

MHDSTS: a new explicit numerical scheme for simulations of partially ionised solar plasma

P. A. González-Morales, E. Khomenko, T. P. Downes, A. de Vicente
Submitted Tuesday 13 March 2018 @ 15:44:28 GMT

The interaction of plasma with magnetic field in the partially ionised solar atmosphere is frequently modelled via a single-fluid approximation, which is valid for the case of a strongly coupled collisional media, such as solar photosphere and low chromosphere. Under the single-fluid formalism the main non-ideal effects are described by a series of extra terms in the generalised induction equation and in the energy conservation equation. These effects are: Ohmic diffusion, ambipolar diffusion, the Hall effect, and the Biermann battery effect. From the point of view of the numerical solution of the single-fluid equations, when ambipolar diffusion or Hall effects dominate can introduce severe restrictions on the integration time step and can compromise the stability of the numerical scheme. In this paper we introduce two numerical schemes to overcome those limitations. The first of them is known as Super Time-Stepping (STS) and it is designed to overcome the limitations imposed when the ambipolar diffusion term is dominant. The second scheme is called the Hall Diffusion Scheme (HDS) and it is used when the Hall term becomes dominant. These two numerical techniques can be used together by applying Strang operator splitting. This paper describes the implementation of the STS and HDS schemes in the single-fluid code Mancha3D. The validation for each of these schemes is provided by comparing the analytical solution with the numerical one for a suite of numerical tests.

[104] arXiv:1803.04888v1 [pdf, vox]

A look at possible microwave dust emission via AKARI infrared all-sky surveys

Aaron C. Bell, Takashi Onaka, Yasuo Doi, Frédéric Galliano, Ronin Wu, Hidehiro Kaneda, Daisuke Ishihara, Martin Giard
Submitted Tuesday 13 March 2018 @ 15:38:30 GMT
4 pages, 3 figures, to appear in proceedings of AKARI Conference 2017, "The Cosmic Wheel and the Legacy of the AKARI Archive: From Galaxies and Stars to Planets and Life", comments welcome

The anomalous microwave emission (AME) still lacks a conclusive explanation. This excess of emission, roughly between 10 and 50 GHz, correlates spatially with interstellar dust, prompting a "spinning dust" hypothesis: electric dipole emission by rapidly rotating, small dust grains. The typical peak frequency range of the AME profile implicates grains on the order of ~1 nm, suggesting polycyclic aromatic hydrocarbon molecules (PAHs). We compare AKARI/Infrared Camera (IRC), with its thorough PAH-band coverage, to AME intensity estimates from the Planck Collaboration, in the {\lambda} Orionis region. We look also at infrared dust emission from other mid IR and far-IR bands. The results and discussion contained here apply to an angular scale of approximately 1{\deg}. In general, our results support an AME-from-dust hypothesis. In {\lambda} Orionis, we find that certainly dust mass correlates with AME, and that PAH-related emission in the AKARI/IRC 9 {\mu}m band may correlate slightly more strongly.

[105] arXiv:1803.04872v1 [pdf, vox]

Project Blue: Visible Light Imaging Search for Terrestrial-class Exoplanets in the Habitable Zones of Alpha Centauri A and B

Jon Morse, Eduardo Bendek, Nathalie Cabrol, Franck Marchis, Margaret Turnbull, Supriya Chakrabarti, Debra Fischer, Colin Goldblatt, Olivier Guyon, Michael Hart, Jared Males, Jim Kasting
Submitted Tuesday 13 March 2018 @ 15:15:46 GMT
5 pages; White paper submitted to the Exoplanet Science Strategy study of the National Academies of Sciences, Engineering and Medicine

Project Blue is designed to deliver a small coronagraphic space telescope mission to low-Earth orbit capable of detecting an Earth-like planet in the habitable zones of the Sun-like stars Alpha Centauri A and B within the next 4 years within a Mission of Opportunity budget envelope. The concept heavily leverages emerging commercial capabilities -- including the telescope optics, spacecraft bus and launch vehicle -- and emphasizes a public-private partnership approach.

[106] arXiv:1803.04869v1 [pdf, vox]

Rapidly evolving transients in the Dark Energy Survey

M. Pursiainen, M. Childress, M. Smith, S. Prajs, M. Sullivan, T. M. Davis, R. J. Foley, T. M. C. Abbott, F. B. Abdalla, S. Allam, J. Annis, J. Asorey, S. Avila, D. Brooks, E. Buckley-Geer, D. L. Burke, J. Calcino, A. Carnero Rosell, D. Carollo, M. Carrasco Kind, J. Carretero, F. J. Castander, C. E. Cunha, C. Curtin, C. B. D'Andrea, C. Davis, J. De Vicente, H. T. Diehl, P. Doel, T. F. Eifler, B. Flaugher, P. Fosalba, J. Frieman, J. García-Bellido, K. Glazebrook, D. Gruen, R. A. Gruendl, C. Gutierrez, G. Gutierrez, W. G. Hartley, S. R. Hinton, D. Hollowood, K. Honscheid, J. K. Hoormann, C. Inserra, D. J. James, T. Jeltema, R. Kessler, A. King, K. Kuehn, N. Kuropatkin, G. Lewis, T. S. Li, C. Lidman, M. Lima, E. Macaulay, M. A. G. Maia, P. Martini, F. Menanteau, A. Möller, R. C. Nichol, R. L. C. Ogando, A. A. Plazas, A. Roodman, M. Sako, E. Sanchez, V. Scarpine, R. Schindler, R. C. Smith, M. Soares-Santos, F. Sobreira, N. E. Sommer, E. Suchyta, E. Swann, M. E. C. Swanson, G. Tarle, B. E. Tucker, D. L. Tucker, S. A. Uddin, A. R. Walker, P. Wiseman, B. Zhang
Submitted Tuesday 13 March 2018 @ 15:07:43 GMT

We present the results of a search for rapidly evolving transients in the Dark Energy Survey Supernova Programme. These events are characterized by fast light curve evolution (rise to peak in $\lesssim 10$ d and exponential decline in $\lesssim30$ d after peak). We discovered 72 events, including 37 transients with a spectroscopic redshift from host galaxy spectral features. The 37 events increase the total number of rapid optical transients by more than factor of two. They are found at a wide range of redshifts ($0.05<z<1.56$) and peak brightnesses ($-15.75>M_\mathrm{g​}>-22.25$). The multiband photometry is well fit by a blackbody up to few weeks after peak. The events appear to be hot ($T\approx10000-3000​0$ K) and large ($R\approx 10^{14}-2\cdot10^{15​}$ cm) at peak, and generally expand and cool in time, though some events show evidence for a receding photosphere with roughly constant temperature. Spectra taken around peak are dominated by a blue featureless continuum consistent with hot, optically thick ejecta. We compare our events with a previously suggested physical scenario involving shock breakout in an optically thick wind surrounding a core-collapse supernova (CCSNe), we conclude that current models for such a scenario might need an additional power source to describe the exponential decline. We find these transients tend to favor star-forming host galaxies, which could be consistent with a core-collapse origin. However, more detailed modeling of the light curves is necessary to determine their physical origin.

[107] arXiv:1803.04833v1 [pdf, vox]

SPH simulations of structures in protoplanetary disks

Tatiana Demidova, Vladimir Grinin
Submitted Tuesday 13 March 2018 @ 14:29:21 GMT
15 pages, 11 figures

The hydrodynamic models of the protoplanetary disk, which perturbed by the embeded low-mass companion, were calculated by our modification of GADGET-2 code. The cases of circular and eccentric orbits which can be coplanar or slightly inclined to the disk midplane were considered. The column density of test particles on the line of sight between the central star and observer was computed during the simulations. Then the column density of the circumstellar dust was calculated under the assumption that the dust and gas are well mixed with a mass ratio 1 : 100. To research the influence of the disk orientation relative to the observer on the circumstellar extinction the calculations were made for four angles of inclination of the line of sight to the disk midplane and eight directions along the azimuth. The column density in the circumstellar and circumbinary disk were computed separately. The calculations have shown the periodic variations of column density can arise both in the circumstellar and circumbinary disks. The amplitude and shape of the variation strongly depend on the parameters of the simulated system (eccentricity and inclination of the orbit, the mass ratio of the companion and star) and its orientation in space. The results of our simulations can be used to explain the cyclic variation of the brightness of young UX Ori type stars.

[108] arXiv:1803.04822v1 [pdf, vox]

A Deep X-ray Survey of the Globular Cluster Omega Centauri

Simon Henleywillis, Adrienne M. Cool, Daryl Haggard, Craig Heinke, Paul Callanan, Yue Zhao
Submitted Tuesday 13 March 2018 @ 14:13:39 GMT

We identify 233 X-ray sources, of which 95 are new, in a 222 ks exposure of Omega Centauri with the Chandra X-ray Observatory's ACIS-I detector. The limiting unabsorbed flux in the core is $f_x$ (0.5$-$6.0 keV) $\simeq$ 3 $\times$ 10$^{-16}$ erg s$^{-1}$ cm$^{-2}$ ($L_X$ $\simeq$ 1 $\times$ 10$^{30}$ erg s$^{-1}$ at 5.2 kpc). We estimate that ~$60\pm 20$ of these are cluster members, of which ~30 lie within the core ($r_c$ $=$ 155 arcsec), and another ~30 between 1$-$2 core radii. We identify four new optical counterparts, for a total of 45 likely identifications. Probable cluster members include 18 cataclysmic variables (CVs) and CV candidates, one quiescent low-mass X-ray binary, four variable stars, and five stars that are either associated with w Cen's anomalous red giant branch, or are sub-subgiants. We estimate that the cluster contains $40\pm 10$ CVs with $L_X$ $>$ 10$^{31}$ erg s$^{-1}$, confirming that CVs are underabundant in w Cen relative to the field. Intrinsic absorption is required to fit X-ray spectra of six of the nine brightest CVs, suggesting magnetic CVs, or high-inclination systems. Though no radio millisecond pulsars (MSPs) are currently known in w Cen, more than 30 unidentified sources have luminosities and X-ray colours like those of MSPs found in other globular clusters; these could be responsible for the Fermi-detected gamma-ray emission from the cluster. Finally, we identify a CH star as the counterpart to the second-brightest X-ray source in the cluster and argue that it is a symbiotic star. This is the first such giant/white dwarf binary to be identified in a globular cluster.

[109] arXiv:1803.04811v1 [pdf, vox]

A Physical Model for the Spectral-Timing Properties of Accreting Black Holes

Ra'ad D. Mahmoud, Chris Done
Submitted Tuesday 13 March 2018 @ 14:01:14 GMT
19 pages, 18 figures, submitted to MNRAS

The rapid X-ray variability of black hole accretion flows in the low/hard state has a strong energy dependence, even looking only above 3 keV where the emission is dominated by Comptonisation. This is clear from the different shapes of the power spectra at different energies, and in the complex pattern of the time lags between distinct energy bands. Our analytic technique fits the energy-dependent power spectra and time lags using a physical model based on fluctuations propagating through a spectrally inhomogeneous flow. The spectral components are set by jointly fitting to the time averaged and Fourier resolved spectra. This framework simultaneously approximates the energy spectra, power spectra in different energy bands and time lags between bands from high quality Cygnus X-1 data where clear structure in the timing statistics is present. We find that the model features demanded by the data are (1) enhanced variability and emission at key radii within the flow, (2) destruction of propagating fluctuations near positions of enhanced turbulence/emission, and (3), stratification of the Comptonising flow into at least three regions, each producing a distinct Compton component. These results establish the importance of specific radii in the Comptonising zone, likely associated with the disc truncation, the inner edge of the flow, and/or the jet launch radius.

[110] arXiv:1803.04809v1 [pdf, vox]

First detection of bromine and antimony in hot stars

K. Werner, T. Rauch, M. Knoerzer, J. W. Kruk
Submitted Tuesday 13 March 2018 @ 13:59:18 GMT
Accepted for publication in A&A

Bromine (atomic number Z=35) and antimony (Z=51) are extremely difficult to detect in stars. In very few instances, weak and mostly uncertain identifications of Br I, Br II, and Sb II in relatively cool, chemically peculiar stars were successful. Adopted solar abundance values rely on meteoritic determinations. Here, we announce the first identification of these species in far-ultraviolet spectra of hot stars (with effective temperatures of 49,500-70,000 K), namely in helium-rich (spectral type DO) white dwarfs. We identify the Br VI resonance line at 945.96 A. A previous claim of Br detection based on this line is incorrect because its wavelength position is inaccurate by about 7 A in atomic databases. Taking advantage of precise laboratory measurements, we identify this line as well as two other, subordinate Br VI lines. Antimony is detected by the Sb V resonance doublet at 1104.23/1225.98 A, as well as two subordinate Sb VI lines. A model-atmosphere analysis reveals strongly oversolar Br and Sb abundances that are caused by radiative-levitation dominated atomic diffusion.

[111] arXiv:1803.04794v1 [pdf, vox]

OH absorption in the first quadrant of the Milky Way as seen by THOR

M. R. Rugel, H. Beuther, S. Bihr, Y. Wang, J. Ott, A. Brunthaler, A. Walsh, S. C. O. Glover, P. F. Goldsmith, L. D. Anderson, N. Schneider, K. M. Menten, S. E. Ragan, J. S. Urquhart, R. S. Klessen, J. D. Soler, N. Roy, J. Kainulainen, T. Henning, F. Bigiel, R. J. Smith, S. N. Longmore
Submitted Tuesday 13 March 2018 @ 13:37:57 GMT
accepted for publication in Astronomy & Astrophysics

The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. This OH study is part of the HI/OH/Recombination line survey (THOR). THOR is a Karl G. Jansky Very Large Array large program of atomic, molecular and ionized gas in the range 15{\deg}$\leq$l$\leq​$67{\deg} and |b|$\leq$1{\deg}. It is the highest-resolution unbiased OH absorption survey to date towards this region. We combine the derived optical depths with literature 13CO(1-0) and HI observations to determine the OH abundance. We detect absorption in the 1665 and 1667 MHz transitions for continuum sources stronger than $F_{\rm cont}\geq$0.1 Jy/beam. OH absorption is found against $\sim$15% of these continuum sources with increasing fractions for stronger sources. Most of the absorption is associated with Galactic HII regions. We find OH and 13CO gas to have similar kinematic properties. The OH abundance decreases with increasing hydrogen column density. The OH abundance with respect to the total hydrogen nuclei column density (atomic and molecular phase) is in agreement with a constant abundance for $A_V$ < 10-20. Towards the lowest column densities, we find sources that exhibit OH absorption but no 13CO emission, indicating that OH is a well suited tracer of the low column density molecular gas. We present spatially resolved OH absorption towards W43. The unbiased nature of the THOR survey opens a new window onto the gas properties of the ISM. The characterization of the OH abundance over a large range of hydrogen gas column densities contributes to the understanding of OH as a molecular gas tracer and provides a starting point for future investigations.

[112] arXiv:1803.04770v1 [pdf, vox]

Spatial Distribution of Globular Clusters in the Galaxy

N. R. Arakelyan, S. V. Pilipenko, N. I. Libeskind
Submitted Tuesday 13 March 2018 @ 13:11:12 GMT
Submitted to MNRAS

The Milky Way's satellite galaxies and Globular Clusters (GCs) are known to exhibit an anisotropic spatial distribution. We examine in detail this anisotropy by the means of the inertia tensor. We estimate the statistical significance of the results by repeating this analysis for random catalogues which use the radial distribution of the real sample. Our method reproduces the well-known planar structure in the distribution of the satellite galaxies. We show that for GCs several anisotropic structures are observed. The GCs at small distances, $2<R<10$ kpc, show a structure coplanar with the Galactic plane. At smaller and larger distances the whole sample of GCs shows quite weak anisotropy. Nevertheless, at largest distances the orientation of the structure is close to that of the satellite galaxies, i.e. perpendicular to the Galactic plane. We estimate the probability of random realization for this structure of 1.7%. The Bulge-Disk GCs show a clear disk-like structure lying within the galactic disk. The Old Halo GCs show two structures: a well pronounced polar elongated structure at $R<3$ kpc which is perpendicular to the galactic plane, and a less pronounced disk-like structure coplanar with the galactic disk at $6<R<20$ kpc. The Young Halo GCs do not show significant anisotropy.

[113] arXiv:1803.04769v1 [pdf, vox]

Coronal Magnetic Structure of Earthbound CMEs and In situ Comparison

Erika Palmerio, Emilia K. J. Kilpua, Christian Möstl, Volker Bothmer, Alexander W. James, Lucie M. Green, Alexey Isavnin, Jackie A. Davies, Richard A. Harrison
Submitted Tuesday 13 March 2018 @ 13:08:08 GMT
27 pages, 6 figures, accepted for publication in Space Weather

Predicting the magnetic field within an Earth-directed coronal mass ejection (CME) well before its arrival at Earth is one of the most important issues in space weather research. In this article, we compare the intrinsic flux rope type, i.e. the CME orientation and handedness during eruption, with the in situ flux rope type for 20 CME events that have been uniquely linked from Sun to Earth through heliospheric imaging. Our study shows that the intrinsic flux rope type can be estimated for CMEs originating from different source regions using a combination of indirect proxies. We find that only 20% of the events studied match strictly between the intrinsic and in situ flux rope types. The percentage rises to 55% when intermediate cases (where the orientation at the Sun and/or in situ is close to 45{\deg}) are considered as a match. We also determine the change in the flux rope tilt angle between the Sun and Earth. For the majority of the cases, the rotation is several tens of degrees, whilst 35% of the events change by more than 90{\deg}. While occasionally the intrinsic flux rope type is a good proxy for the magnetic structure impacting Earth, our study highlights the importance of capturing the CME evolution for space weather forecasting purposes. Moreover, we emphasize that determination of the intrinsic flux rope type is a crucial input for CME forecasting models.

[114] arXiv:1803.05329v1 [pdf, vox]

Revealing neutral bremsstrahlung in two-phase argon electroluminescence

A. Buzulutskov, E. Shemyakina, A. Bondar, A. Dolgov, E. Frolov, V. Nosov, V. Oleynikov, L. Shekhtman, A. Sokolov
Submitted Tuesday 13 March 2018 @ 11:55:42 GMT
12 pages, 20 figures

Proportional electroluminescence (EL) in noble gases has long been used in two-phase detectors for dark matter search, to record ionization signals induced by particle scattering in the noble-gas liquid (S2 signals). Until recently, it was believed that proportional electroluminescence was fully due to VUV emission of noble gas excimers produced in atomic collisions with excited atoms, the latter being in turn produced by drifting electrons. In this work we consider an additional mechanism of proportional electroluminescence, namely that of bremsstrahlung of drifting electrons scattered on neutral atoms (so-called neutral bremsstrahlung); it is systemically studied here both theoretically and experimentally. In particular, the absolute EL yield has for the first time been measured in pure gaseous argon in the two-phase mode, using a dedicated two-phase detector with EL gap optically read out by cryogenic PMTs and SiPMs. We show that the neutral bremsstrahlung effect can explain two intriguing observations in EL radiation: that of the substantial contribution of the non-VUV spectral component, extending from the UV to NIR, and that of the photon emission at lower electric fields, below the Ar excitation threshold. Possible applications of neutral bremsstrahlung effect in two-phase dark matter detectors are discussed.

[115] arXiv:1803.04734v1 [pdf, vox]

The Dramatic Size and Kinematic Evolution of Massive Early-Type Galaxies

A. Lapi, L. Pantoni, L. Zanisi, J. Shi, C. Mancuso, M. Massardi, F. Shankar, A. Bressan, L. Danese
Submitted Tuesday 13 March 2018 @ 11:25:03 GMT
28 pages, 10 figures. Accepted by ApJ

[ABRIDGED] We aim to provide a holistic view on the typical size and kinematic evolution of massive early-type galaxies (ETGs), that encompasses their high-$z$ star-forming progenitors, their high-$z$ quiescent counterparts, and their configurations in the local Universe. Our investigation covers the main processes playing a relevant role in the cosmic evolution of ETGs. Specifically, their early fast evolution comprises: biased collapse of the low angular momentum gaseous baryons located in the inner regions of the host dark matter halo; cooling, fragmentation, and infall of the gas down to the radius set by the centrifugal barrier; further rapid compaction via clump/gas migration toward the galaxy center, where strong heavily dust-enshrouded star-formation takes place and most of the stellar mass is accumulated; ejection of substantial gas amount from the inner regions by feedback processes, which causes a dramatic puffing up of the stellar component. In the late slow evolution, passive aging of stellar populations and mass additions by dry merger events occur. We describe these processes relying on prescriptions inspired by basic physical arguments and by numerical simulations, to derive new analytical estimates of the relevant sizes, timescales, and kinematic properties for individual galaxies along their evolution. Then we obtain quantitative results as a function of galaxy mass and redshift, and compare them to recent observational constraints on half-light size $R_e$, on the ratio $v/\sigma$ between rotation velocity and velocity dispersion (for gas and stars) and on the specific angular momentum $j_\star$ of the stellar component; we find good consistency with the available multi-band data in average values and dispersion, both for local ETGs and for their $z\sim 1-2$ star-forming and quiescent progenitors.

[116] arXiv:1803.04733v1 [pdf, vox]

Gas, Dust, Stars, Star Formation and their Evolution in M33 at Giant Molecular Cloud Scales

Shinya Komugi, Rie E. Miura, Nario Kuno, Tomoka Tosaki
Submitted Tuesday 13 March 2018 @ 11:20:21 GMT
9 pages, 3 figures, accepted for publication in PASJ

We report on a multi parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M33. A catalog of GMCs identifed in 12CO(J=3-2) was used to compile associated 12CO(J=1-0), dust, stellar mass and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components PC1 and PC2 which retain 75% of the information in the original dataset. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (<10Myr) GMCs occupy a distinct region in the PC1-PC2 plane, with lower ISM content and star formation activity compared to intermediate age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ~10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt Kennicutt relation with the molecular gas term substituted by dust.

[117] arXiv:1803.04728v1 [pdf, vox]

Study of Three-Dimensional Magnetic Structure and the Successive Eruptive Nature of Active Region 12371

P. Vemareddy, P. Demóulin
Submitted Tuesday 13 March 2018 @ 11:03:44 GMT
16 pages, 11 Figures; Accepted in ApJ

We study the magnetic structure of successively erupting sigmoid in active region 12371 by modeling the quasi-static coronal field evolution with non-linear force-free field (NLFFF) equilibria. HMI/SDO vector magnetograms are used as input to the NLFFF model. In all eruption events, the modeled structure resembles the observed pre-eruptive coronal sigmoid and the NLFFF core-field is a combination of double inverse J-shaped and inverse-S field-lines with dips touching the photosphere. Such field-lines are formed by flux-cancellation reconnection of opposite-J field-lines at bald-patch locations. It implies the formation of a weakly twisted flux-rope from large scale sheared arcade field lines. Later on, this flux-rope undergo coronal tether-cutting reconnection until a CME is triggered. The modeled structure captured these major features of sigmoid-to-arcade-to​-sigmoid transformation, that is being recurrent under continuous photospheric flux motions. Calculations of the field-line twist reveal a fractional increase followed by a decrease of the number of pixels having a range of twist. This traces the buildup process of a twisted core-field by slow photospheric motions and the relaxation after eruption, respectively. Our study infers that the large eruptivity of this AR is due to a steep decrease of the background coronal field meeting the torus instability criteria at low height ($\approx 40$ Mm) in contrast to non-eruptive ARs.

[118] arXiv:1803.04716v1 [pdf, vox]

Cosmic clocks: A Tight Radius - Velocity Relationship for HI-Selected Galaxies

Gerhardt R. Meurer, Danail Obreschkow, O. Ivy Wong, Zheng Zheng, Fiona M. Audcent-Ross, D. J. Hanish
Submitted Tuesday 13 March 2018 @ 10:33:16 GMT
14 pages, 7 figures, 3 in colour. Published in MNRAS

HI-Selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and HI emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts of their discs. Observations of a large optically-selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear RV relationship is expected from simple models of galaxy formation and evolution. The total mass within Rmax has collapsed by a factor of 37 compared to the present mean density of the Universe. Adopting standard assumptions we find a mean halo spin parameter lambda in the range 0.020 to 0.035. The dispersion in lambda, 0.16 dex, is smaller than expected from simulations. This may be due to the biases in our selection of disc galaxies rather than all halos. The estimated mass densities of stars and atomic gas at Rmax are similar (~0.5 Msun/pc^2) indicating outer discs are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio between Rmax and disc scale length is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution or a combination thereof.

[119] arXiv:1803.04709v1 [pdf, vox]

Interactions of twisted $Ω$-loops in a model solar convection zone

L. Jouve, A. S. Brun, G. Aulanier
Submitted Tuesday 13 March 2018 @ 10:05:18 GMT
39 pages, 20 figures, accepted for publication in ApJ

This study aims at investigating the ability of strong interactions between magnetic field concentrations during their rise through the convection zone to produce complex active regions at the solar surface. To do so, we perform numerical simulations of buoyant magnetic structures evolving and interacting in a model solar convection zone. We first produce a 3D model of rotating convection and then introduce idealized magnetic structures close to the bottom of the computational domain. These structures possess a certain degree of field line twist and they are made buoyant on a particular extension in longitude. The resulting twisted $\Omega$-loops will thus evolve inside a spherical convective shell possessing large-scale mean flows. We present results on the interaction between two such loops with various initial parameters (mainly buoyancy and twist) and on the complexity of the emerging magnetic field. In agreement with analytical predictions, we find that if the loops are introduced with opposite handedness and same axial field direction or same handedness but opposite axial field, they bounce against each other. The emerging region is then constituted of two separated bipolar structures. On the contrary, if the loops are introduced with the same direction of axial and peripheral magnetic fields and if sufficiently close, they merge while rising. This more interesting case produces complex magnetic structures, with a high degree of non-neutralized currents, especially when the convective motions act significantly on the magnetic field. This indicates that those interactions could be good candidates to produce eruptive events like flares or CMEs.

[120] arXiv:1803.04697v1 [pdf, vox]

ALPS: The Arbitrary Linear Plasma Solver

Daniel Verscharen, Kristopher G. Klein, Benjamin D. G. Chandran, Michael L. Stevens, Chadi S. Salem, Stuart D. Bale
Submitted Tuesday 13 March 2018 @ 09:29:53 GMT
26 pages, 13 figures, submitted

The Arbitrary Linear Plasma Solver (ALPS) is a parallelised numerical code that solves the dispersion relation in a hot (even relativistic) magnetised plasma with an arbitrary number of particle species with arbitrary gyrotropic equilibrium distribution functions for any direction of wave propagation with respect to the background field. ALPS reads the background momentum distributions as tables of values on a $(p_{\perp},p_{\para​llel})$ grid, where $p_{\perp}$ and $p_{\parallel }$ are the momentum coordinates in the directions perpendicular and parallel to the background magnetic field, respectively. We present the mathematical and numerical approach used by ALPS and introduce our algorithms for the handling of poles and the analytic continuation for the Landau contour integral. We then show test calculations of dispersion relations for a selection of stable and unstable configurations in Maxwellian, bi-Maxwellian, $\kappa$-distributed​, and J\"uttner-distribute​d plasmas. These tests demonstrate that ALPS derives reliable plasma dispersion relations. ALPS will make it possible to determine the properties of waves and instabilities in the non-equilibrium plasmas that are frequently found in space, laboratory experiments, and numerical simulations.

[121] arXiv:1803.04693v1 [pdf, vox]

Liouville term for neutrinos: Flavor structure and wave interpretation

Tobias Stirner, Günter Sigl, Georg Raffelt
Submitted Tuesday 13 March 2018 @ 09:21:11 GMT

Neutrino production, absorption, transport, and flavor evolution in astrophysical environments is described by a kinetic equation $D\varrho=-i[{\sf H},\varrho]+{\cal C}[\varrho]$. Its basic elements are generalized occupation numbers $\varrho$, matrices in flavor space, that depend on time $t$, space $\bf x$, and momentum $\bf p$. The commutator expression encodes flavor conversion in terms of a matrix $\sf H$ of oscillation frequencies, whereas ${\cal C}[\varrho]$ represents source and sink terms as well as collisions. The Liouville operator on the left hand side involves linear derivatives in $t$, $\bf x$ and $\bf p$. The simplified expression $D=\partial_t+\hat{\​bf p}\cdot{\partial}_{\​bf x}$ for ultra-relativistic neutrinos was recently questioned in that flavor-dependent velocities should appear instead of the unit vector $\hat{\bf p}$. Moreover, a new damping term was postulated as a result. We here derive the full flavor-dependent velocity structure of the Liouville term although it appears to cause only higher-order corrections. Moreover, we argue that on the scale of the neutrino oscillation length, the kinetic equation can be seen as a first-order wave equation.

[122] arXiv:1803.04692v1 [pdf, vox]

Can a bright and energetic X-ray pulsar be hiding amid the debris of SN 1987A?

P. Esposito, N. Rea, D. Lazzati, M. Matsuura, R. Perna, J. A. Pons
Submitted Tuesday 13 March 2018 @ 09:20:07 GMT
Accepted for publication in the Astrophysical Journal; 10 pages, 3 color figures, 2 tables

The mass of the stellar precursor of supernova (SN) 1987A and the burst of neutrinos observed at the moment of the explosion are consistent with the core-collapse formation of a neutron star. However, no compelling evidence for the presence in SN 1987A of a compact object of any kind has been found yet in any band of the electromagnetic spectrum, prompting questions on whether the neutron star survived and, if it did, on its properties. Starting from the analysis of recent Chandra observations, here we appraise the current observational situation. We derived limits on the X-ray luminosity of a compact object with a nonthermal, Crab-pulsar-like spectrum of the order of $\approx$$(1$-$5)\ti​mes10^{35}$ erg s$^{-1}$, corresponding to limits on the rotational energy loss of a possible X-ray pulsar in SN 1987A of $\approx$$(0.5$-$1.5​)\times10^{38}$ erg s$^{-1}$. However, a much brighter X-ray source cannot be excluded if, as is likely, it is enshrouded in a cloud of absorbing matter with metallicity similar to that expected in the outer layers of a massive star towards the end of its life. We found that other limits obtained from various arguments and observations in other energy ranges either are unbinding or allow a similar maximum luminosity of the order of $\approx$$10^{35}$ erg s$^{-1}$. We conclude that while a pulsar alike the one in the Crab Nebula in both luminosity and spectrum is hardly compatible with the observations, there is ample space for an `ordinary' X-ray-emitting young neutron star, born with normal initial spin period, temperature and magnetic field, to be hiding inside the evolving remnant of SN 1987A.

[123] arXiv:1803.04690v1 [pdf, vox]

Outflowing OH$^+$ in Markarian 231: the ionization rate of the molecular gas

E. González-Alfonso, J. Fischer, S. Bruderer, M. L. N. Ashby, H. A. Smith, S. Veilleux, H. S. P. Müller, K. P. Stewart, E. Sturm
Submitted Tuesday 13 March 2018 @ 09:13:28 GMT
25 pages, 11 figures

The oxygen-bearing molecular ions OH+, H2O+, and H3O+ are key species that probe the ionization rate of (partially) molecular gas that is ionized by X-rays and cosmic rays permeating the interstellar medium. We report Herschel far-infrared and submillimeter spectroscopic observations of OH+ in Mrk 231, showing both ground-state P-Cygni profiles, and excited line profiles with blueshifted absorption wings extending up to ~1000 km s^{-1}. In addition, OH+ probes an excited component peaking at central velocities, likely arising from the torus probed by the OH centimeter-wave megamaser. Four lines of H2O+ are also detected at systemic velocities, but H3O+ is undetected. Based on our earlier OH studies, we estimate an abundance ratio of OH/OH+~5-10 for the outflowing components and ~20 for the torus, and an OH+ abundance relative to H nuclei of ~>10^{-7}. We also find high OH+/H2O+ and OH+/H3O+ ratios, both are ~>4 in the torus and ~>10-20 in the outflowing gas components. Chemical models indicate that these high OH+ abundances relative to OH, H2O+, and H3O+ are characteristic of gas with a high ionization rate per unit density, \zeta/n_H~(1-5)x10^{​-17} cm^3 s^{-1} and ~(1-2)x10^{-16} cm^3 s^{-1} for the above components, respectively, and an ionization rate of \zeta~(0.5-2)x10^{-1​2} s^{-1}. X-rays appear to be unable to explain the inferred ionization rate, and thus we suggest that low-energy (10-400 MeV) cosmic-rays are primarily responsible for the ionization with \dot{M}_{CR}~0.01 M_{sun} yr^{-1} and \dot{E}_{CR}~10^{44} erg s^{-1}, the latter corresponding to 1% of the AGN luminosity and similar to the energetics of the molecular outflow. We suggest that cosmic-rays accelerated in the forward shock associated with the molecular outflow are responsible for the ionization, as they diffuse through the outflowing molecular phase downstream.

[124] arXiv:1803.04686v1 [pdf, vox]

Current status and desired accuracy of the isotopic production cross sections relevant to astrophysics of cosmic rays I. Li, Be, B, C, N

Yoann Genolini, David Maurin, Igor V. Moskalenko, Michael Unger
Submitted Tuesday 13 March 2018 @ 08:59:44 GMT
37 pages, many figures and tables. Comments are welcome

The accuracy of the current generation of cosmic-ray (CR) experiments, such as AMS-02, PAMELA, CALET, and ISS-CREAM, is now reaching $\sim$1--3\% in a wide range in energy per nucleon from GeV/n to multi-TeV/n. Their correct interpretation could potentially lead to discoveries of new physics and subtle effects that were unthinkable just a decade ago. However, a major obstacle in doing so is the current uncertainty in the isotopic production cross sections that can be as high as 20--50\% or even larger in some cases. While there is a recently reached consensus in the astrophysics community that new measurements of cross sections are desirable, no attempt to evaluate the importance of particular reaction channels and their required accuracy has been made yet. It is, however, clear that it is a huge work that requires an incremental approach. The goal of this study is to provide the ranking of the isotopic cross sections contributing to the production of the most astrophysically important CR Li, Be, B, C, and N species. In this paper, we (i) rank the reaction channels by their importance for a production of a particular isotope, (ii) provide comparisons plots between the models and data used, and (iii) evaluate a generic beam time necessary to reach a 3\% precision in the production cross-sections pertinent to the AMS-02 experiment. This first roadmap may become a starting point in the planning of new measurement campaigns that could be carried out in several nuclear and/or particle physics facilities around the world. A comprehensive evaluation of other isotopes $Z\leq30$ will be a subject of follow-up studies.

[125] arXiv:1803.03002v2 [pdf, vox]

Energy budget of cosmological first-order phase transition in FLRW background

Rong-Gen Cai, Shao-Jiang Wang
Submitted Tuesday 13 March 2018 @ 07:46:19 GMT
v1, 36 pages, 8 figures; v2, 37 pages, 8 figures, major change of conclusion whose application range has shrunk down to the case of slow first-order phase transition, added reference and acknowledgement

We study the hydrodynamics of bubble expansion in cosmological first-order phase transition in the Friedmann-Lema\^{\i}​tre-Robertson-Walker​ (FLRW) background with probe limit. Different from previous studies for fast first-order phase transition in flat background, we find that, for slow first-order phase transition in FLRW background with given peculiar velocity of bubble wall, the efficiency factor of energy transfer into bulk motion of thermal fluid is significantly reduced, thus decreasing the previously-thought dominated contribution from sound wave to the stochastic gravitational-wave background.

[126] arXiv:1803.04642v1 [pdf, vox]

The value of astrometry for exoplanet science

Eduardo Bendek, Mark Marley, Michael Shao, Olivier Guyon, Ruslan Belikov, Peter Tuthill
Submitted Tuesday 13 March 2018 @ 06:17:09 GMT

Exoplanets mass measurements will be a critical next step to assess the habitability of Earth-like planets: a key aspect of the 2020 vision in the previous decadal survey and also central to NASA's strategic priorities. Precision astrometry delivers measurement of exoplanet masses, allowing discrimination of rocky planets from water worlds and enabling much better modeling of their atmosphere improving species retrieval from spectroscopy. The scientific potential of astrometry will be enormous. The intrinsic astrophysical noise floor set by star spots and stellar surface activity is about a factor of ten more benign for astrometry than for the more established technique of Radial Velocity, widening the discovery region and pushing detection thresholds to lower masses than previously possible. On the instrumental side, precision astrometry is limited by optical field distortion and detector calibration issues. Both technical challenges are now being addressed successfully in the laboratory. However, we have identified the need to continue these technology development efforts to achieve sub-microarcsecond astrometry precision necessary for detection and characterization of Earth-like planets around nearby FGK stars. The international community has realized the importance of astrometry, and various astrometry missions have been proposed and under development, with a few high profile missions now operational. We believe that it is vital for the U.S. scientific community to participate in the development of these new technologies and scientific discoveries. We recommend exploring alternatives to incorporate astrometric capabilities into future exoplanet flagship missions such as HABEX and LUVOIR, substantially increasing the scientific return associated with the expected yield of earth-like planets to be recovered.

[127] arXiv:1803.04601v1 [pdf, vox]

Suzaku Observations of Low Surface Brightness Cluster Abell 1631

Yasunori Babazaki, Ikuyuki Mitsuishi, Naomi Ota, Shin Sasaki, Hans Boehringer, Gayoung Chon, Gabriel W. Pratt, Hironori Matsumoto
Submitted Tuesday 13 March 2018 @ 02:48:38 GMT
18 pages, 4 figures, accepted for publication in PASJ

We present analysis results for a nearby galaxy cluster Abell 1631 at $z~=~0.046$ using the X-ray observatory Suzaku. This cluster is categorized as a low X-ray surface brightness cluster. To study the dynamical state of the cluster, we conduct four-pointed Suzaku observations and investigate physical properties of the Mpc-scale hot gas associated with the A1631 cluster for the first time. Unlike relaxed clusters, the X-ray image shows no strong peak at the center and an irregular morphology. We perform spectral analysis and investigate the radial profiles of the gas temperature, density, and entropy out to approximately 1.5~Mpc in the east, north, west, and south directions by combining with the XMM-Newton data archive. The measured gas density in the central region is relatively low (${\rm a~few} \times~10^{-4}~{\rm cm^{-3}}$) at the given temperature ($\sim2.9~{\rm keV}$) compared with X-ray-selected clusters. The entropy profile and value within the central region ($r<0.1~r_{200}$) are found to be flatter and higher ($\gtrsim400~ {\rm keV~cm}^2$). The observed bolometric luminosity is approximately three times lower than that expected from the luminosity-temperatu​re relation in previous studies for relaxed clusters. These features are also observed in another low surface brightness cluster, Abell 76. The spatial distributions of galaxies and the hot gas appear to be different. The X-ray luminosity is relatively lower than that expected from the velocity dispersion. A post-merger scenario may explain the observed results.

[128] arXiv:1803.04600v1 [pdf, vox]

LAB4D: A Low Power, Multi-GSa/s, Transient Digitizer with Sampling Timebase Trimming Capabilities

Jarred M. Roberts, Eric Oberla, Patrick Allison, Gary S. Varner, Stefan Spack, Brendan Fox, Ben Rotter
Submitted Tuesday 13 March 2018 @ 02:39:09 GMT

The LAB4D is a new application-specific integrated circuit (ASIC) of the Large Analog Bandwidth Recorder and Digitizer with Ordered Readout (LABRADOR) family, for use in direct wideband radio frequency digitization such as is used in ultrahigh energy neutrino and cosmic ray astrophysics. The LAB4D is a single channel switched-capacitor array (SCA) 12-bit sampler with integrated analog-to-digital converters (ADC), developed in the TSMC 0.25um process. The LAB4D, operating at 3.2GSa/s, contains 4096 total samples arranged in 32 windows, for a total record length of 1280ns. The 3dB bandwidth is approximately 1.3GHz, with a directly-coupled 50ohm input. This represents a factor of 16 increase in the sample depth and an increase in analog bandwidth and sampling depth in comparison to the previous generation LAB3 digitizer. Individually addressable windows allow for sampling and digitization to occur simultaneously, leading to nearly deadtime-free readout for kHz readout rates. All biases and current references are generated via internal digital-to-analog converters (DACs), resulting in a stand-alone digitizer with no additional support circuitry. In addition, the LAB4D contains sample cell timebase trimming capabilities, reducing the intrinsic sample-to-sample time variance to less than 5ps; an improvement of about 80%. This allows the LAB4D to be used in precision timing applications with minimal post-hoc calibration.

Submitted Mon, 12 Mar 2018

[129] arXiv:1803.04564v1 [pdf, vox]

NASA's Asteroid Grand Challenge: Strategy, Results and Lessons Learned

Jennifer L Gustetic, Victoria Friedensen, Jason L Kessler, Shanessa Jackson, James Parr
Submitted Monday 12 March 2018 @ 22:55:35 GMT

Beginning in 2012, NASA utilized a strategic process to identify broad societal questions, or grand challenges, that are well suited to the aerospace sector and align with national priorities. This effort generated NASA's first grand challenge, the Asteroid Grand Challenge, a large scale effort using multidisciplinary collaborations and innovative engagement mechanisms focused on finding and addressing asteroid threats to human populations. In April 2010, President Barack Obama announced a mission to send humans to an asteroid by 2025. This resulted in the agency's Asteroid Redirect Mission to leverage and maximize existing robotic and human efforts to capture and reroute an asteroid, with the goal of eventual human exploration. The AGC, initiated in 2013, complemented ARM by expanding public participation, partnerships, and other approaches to find, understand, and overcome these potentially harmful asteroids. This paper describes a selection of AGC activities implemented from 2013 to 2017 and their results, excluding those conducted by NASA's Near Earth Object Observations Program and other organizations. The strategic development of the initiative is outlined as well as initial successes, strengths, and weaknesses resulting from the first four years of AGC activities and approaches. Finally, we describe lesson learned and areas for continued work and study. The AGC lessons learned and strategies could inform the work of other agencies and organizations seeking to conduct a global scientific investigation with matrixed organizational support, multiple strategic partners, and numerous internal and external open innovation approaches and audiences.

[130] arXiv:1803.04563v1 [pdf, vox]

On The Nature of ultra-faint Dwarf Galaxy Candidates II: The case of Cetus II

Blair C. Conn, Helmut Jerjen, Dongwon Kim, Mischa Schirmer
Submitted Monday 12 March 2018 @ 22:54:46 GMT
12 pages, 12 figures, Accepted for publication in ApJ

We obtained deep Gemini GMOS-S $g,r$ photometry of the ultra-faint dwarf galaxy candidate Cetus II with the aim of providing stronger constraints on its size, luminosity and stellar population. Cetus II is an important object in the size-luminosity plane as it occupies the transition zone between dwarf galaxies and star clusters. All known objects smaller than Cetus II ($r_h \sim 20$ pc) are reported to be star clusters, while most larger objects are likely dwarf galaxies. We found a prominent excess of main-sequence stars in the colour-magnitude diagram of Cetus II, best described by a single stellar population with an age of 11.2 Gyr, metallicity of [Fe/H] = $-1.28$ dex, an [$\alpha$/Fe] = 0.0 dex at a heliocentric distance of 26.3$\pm$1.2 kpc. As well as being spatially located within the Sagittarius dwarf tidal stream, these properties are well matched to the Sagittarius galaxy's Population B stars. Interestingly, like our recent findings on the ultra-faint dwarf galaxy candidate Tucana V, the stellar field in the direction of Cetus II shows no evidence of a concentrated overdensity despite tracing the main sequence for over six magnitudes. These results strongly support the picture that Cetus II is not an ultra-faint stellar system in the Milky Way halo, but made up of stars from the Sagittarius tidal stream.

[131] arXiv:1803.05313v1 [pdf, vox]

Variable stars in NGC 4147 revisited: RR Lyrae stars new CCD VI photometry and physical parameters

A. Arellano Ferro, F. C. Rojas Galindo, S. Muneer, Sunetra Giridhar
Submitted Monday 12 March 2018 @ 21:54:10 GMT
7 pages, 5 tables, 4 figures. arXiv admin note: text overlap with arXiv:1709.00044

We have calculated the physical parameters of the RR Lyrae stars in the globular cluster NGC~4147 via the Fourier decomposition of their light curves, using new data and well-established semi-empirical calibrations and zero points. The mean metallicity and distance estimated using the RRc stars are [Fe/H]$_{ZW}=-1.72\p​m0.15$ and $19.05\pm0.46$ kpc respectively. The star V18, whose variability has been previously in dispute, is confirmed to be a variable of the SR type with a period of about 24.8d, and it has been used to get and independent distance estimate of the cluster. It is observed that the RRab and RRc stars do not share the inter-mode region in the horizontal branch. The cluster can be classified as of intermediate Oosterhoff type. Its horizontal branch structure and metallicity make a good case for extragalactic origin. It follows the distribution of Oo~I type globular clusters in the $M_V-$[Fe/H] plane, as depicted from the RRc stars.

[132] arXiv:1803.04543v1 [pdf, vox]

Possible Bright Starspots on TRAPPIST-1

Brett M. Morris, Eric Agol, James R. A. Davenport, Suzanne L. Hawley
Submitted Monday 12 March 2018 @ 21:33:52 GMT
Accepted by ApJ March 12, 2018

The M8V star TRAPPIST-1 hosts seven roughly Earth-sized planets and is a promising target for exoplanet characterization. Kepler/K2 Campaign 12 observations of TRAPPIST-1 in the optical show an apparent rotational modulation with a 3.3 day period, though that rotational signal is not readily detected in the Spitzer light curve at 4.5 $\mu$m. If the rotational modulation is due to starspots, persistent dark spots can be excluded from the lack of photometric variability in the Spitzer light curve. We construct a photometric model for rotational modulation due to photospheric bright spots on TRAPPIST-1 which is consistent with both the Kepler and Spitzer light curves. The maximum-likelihood model with three spots has typical spot sizes of $R_\mathrm{spot}/R_\​star \approx 0.004$ at temperature $T_\mathrm{spot} \gtrsim 5300 \pm 200$ K. We also find that large flares are observed more often when the brightest spot is facing the observer, suggesting a correlation between the position of the bright spots and flare events. In addition, these flares may occur preferentially when the spots are increasing in brightness, which suggests that the 3.3 d periodicity may not be a rotational signal, but rather a characteristic timescale of active regions.

[133] arXiv:1803.04541v1 [pdf, vox]

Probing secret interactions of eV-scale sterile neutrinos with the diffuse supernova neutrino background

Yu Seon Jeong, Sergio Palomares-Ruiz, Mary Hall Reno, Ina Sarcevic
Submitted Monday 12 March 2018 @ 21:19:14 GMT
47 pages, 9 figures

Sterile neutrinos with mass in the eV-scale and large mixings of order $\theta_0\simeq 0.1$ could explain some anomalies found in short-baseline neutrino oscillation data. Here, we revisit a neutrino portal scenario in which eV-scale sterile neutrinos have self-interactions via a new gauge vector boson $\phi$. Their production in the early Universe via mixing with active neutrinos can be suppressed by the induced effective potential in the sterile sector. We study how different cosmological observations can constrain this model, in terms of the mass of the new gauge boson, $M_\phi$, and its coupling to sterile neutrinos, $g_s$. Then, we explore how to probe part of the allowed parameter space of this particular model with future observations of the diffuse supernova neutrino background by the Hyper-Kamiokande and DUNE detectors. For $M_\phi \sim 5-10$~keV and $g_s \sim 10^{-4}-10^{-2}$, as allowed by cosmological constraints, we find that interactions of diffuse supernova neutrinos with relic sterile neutrinos on their way to the Earth would result in significant dips in the neutrino spectrum which would produce unique features in the event spectra observed in these detectors.

[134] arXiv:1803.04538v1 [pdf, vox]

Detection of a population of carbon-enhanced metal-poor stars in the Sculptor dwarf spheroidal galaxy

Anirudh Chiti, Joshua D. Simon, Anna Frebel, Ian B. Thompson, Stephen A. Shectman, Mario Mateo, John I. Bailey III, Jeffrey D. Crane, Matthew Walker
Submitted Monday 12 March 2018 @ 21:17:16 GMT
20 pages, 14 figures, 6 tables. Accepted for publication in ApJ

The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present metallicity and carbon abundance measurements of 100 stars in Sculptor from medium-resolution (R ~ 2000) spectra taken with the Magellan/Michigan Fiber System mounted on the Magellan-Clay 6.5m telescope at Las Campanas Observatory. We identify 24 extremely metal-poor star candidates ([Fe/H] $< -3.0$) and 21 carbon-enhanced metal-poor (CEMP) star candidates. Eight carbon-enhanced stars are classified with at least 2$\sigma$ confidence and five are confirmed as such with follow-up R~6000 observations using the Magellan Echellette Spectrograph on the Magellan-Baade 6.5m telescope. We measure a CEMP fraction of 36% for stars below [Fe/H] = -3.0, indicating that the prevalence of carbon-enhanced stars in Sculptor is similar to that of the halo (~43%) after excluding likely CEMP-s and CEMP-r/s stars from our sample. However, we do not detect that any CEMP stars are strongly enhanced in carbon (e.g., [C/Fe] $>$ 1.0). The existence of a large number of CEMP stars both in the halo and in Sculptor suggests that some halo CEMP stars may have originated from accreted early analogs of dwarf galaxies.

[135] arXiv:1803.04527v1 [pdf, vox]

Rise of the First Super-Massive Stars

John A. Regan, Turlough P. Downes
Submitted Monday 12 March 2018 @ 20:53:01 GMT
13 pages, 9 figures. Submitted to MNRAS. Comments welcome

We use high resolution adaptive mesh refinement simulations to model the formation of massive metal-free stars in the early Universe. By applying Lyman-Werner (LW) backgrounds of 100 J$_{21}$ and 1000 J$_{21}$ respectively we construct environments conducive to the formation of massive stars. We find that only in the case of the higher LW backgrounds are super-critical accretion rates realised that are necessary for super-massive star (SMS) formation. Mild fragmentation is observed for both backgrounds. Violent dynamical interactions between the stars that form in the more massive halo formed (1000 J$_{21}$ background) results in the eventual expulsion of the two most massive stars from the halo. In the smaller mass halo (100 J$_{21}$ background) mergers of stars occur before any multibody interactions and a single massive Pop III star is left at the centre of the halo at the end of our simulation. Feedback from the very massive Pop III stars is not effective in generating a large HII region with ionising photons absorbed within a few thousand AU of the star. In all cases a massive black hole seed is the expected final fate of the most massive objects. The seed of the massive Pop III star which remained at the centre of the less massive halo experiences steady accretion rates of almost $10^{-2}$ M$_{\odot}$/yr and if these rates continue could potentially experience super-Eddington accretion rates in the immediate aftermath of collapsing into a black hole.

[136] arXiv:1803.04526v1 [pdf, vox]

Kepler Data Validation I -- Architecture, Diagnostic Tests, and Data Products for Vetting Transiting Planet Candidates

Joseph D. Twicken, Joseph H. Catanzarite, Bruce D. Clarke, Forrest Girouard, Jon M. Jenkins, Todd C. Klaus, Jie Li, Sean D. McCauliff, Shawn E. Seader, Peter Tenenbaum, Bill Wohler, Stephen T. Bryson, Christopher J. Burke, Douglas A. Caldwell, Michael R. Haas, Christopher E. Henze, Dwight T. Sanderfer
Submitted Monday 12 March 2018 @ 20:52:32 GMT
84 pages, 26 figures, 2 tables. Accepted for publication in PASP on 9 March 2018

The Kepler Mission was designed to identify and characterize transiting planets in the Kepler Field of View and to determine their occurrence rates. Emphasis was placed on identification of Earth-size planets orbiting in the Habitable Zone of their host stars. Science data were acquired for a period of four years. Long-cadence data with 29.4 min sampling were obtained for ~200,000 individual stellar targets in at least one observing quarter in the primary Kepler Mission. Light curves for target stars are extracted in the Kepler Science Data Processing Pipeline, and are searched for transiting planet signatures. A Threshold Crossing Event is generated in the transit search for targets where the transit detection threshold is exceeded and transit consistency checks are satisfied. These targets are subjected to further scrutiny in the Data Validation (DV) component of the Pipeline. Transiting planet candidates are characterized in DV, and light curves are searched for additional planets after transit signatures are modeled and removed. A suite of diagnostic tests is performed on all candidates to aid in discrimination between genuine transiting planets and instrumental or astrophysical false positives. Data products are generated per target and planet candidate to document and display transiting planet model fit and diagnostic test results. These products are exported to the Exoplanet Archive at the NASA Exoplanet Science Institute, and are available to the community. We describe the DV architecture and diagnostic tests, and provide a brief overview of the data products. Transiting planet modeling and the search for multiple planets on individual targets are described in a companion paper. The final revision of the Kepler Pipeline code base is available to the general public through GitHub. The Kepler Pipeline has also been modified to support the TESS Mission which will commence in 2018.

[137] arXiv:1803.04515v1 [pdf, vox]

Unveiling the physical conditions of the youngest disks: A warm embedded disk in L1527

Merel L. R. van 't Hoff, John J. Tobin, Daniel Harsono, Ewine F. van Dishoeck
Submitted Monday 12 March 2018 @ 20:32:15 GMT
16 pages, 13 figures, 2 tables (and 5 pages of appendix with 8 figures). Accepted for publication in A&A

[Abridged] Protoplanetary disks have been studied extensively, both physically and chemically, to understand the environment in which planets form. However, the first steps of planet formation are likely to occur already when the protostar and disk are still embedded in their natal envelope. The initial conditions for planet formation may thus be provided by these young embedded disks, of which the physical and chemical structure is poorly characterized. We aim to constrain the midplane temperature structure, one of the critical unknowns, of the embedded disk around L1527. In particular, we set out to determine whether there is an extended cold outer region where CO is frozen out, as is the case for Class II disks. We use archival ALMA data to directly observe the midplane of the near edge-on L1527 disk. Optically thick $^{13}$CO ($J=2-1$) and C$^{18}$O ($J=2-1$) emission is observed throughout the disk and inner envelope, while N$_2$D$^+ (J=3-2$), which can only be abundant when CO is frozen out, is not detected. Both CO isotopologues have brightness temperatures $\gtrsim$ 25 K along the midplane. Disk and envelope emission can be disentangled kinematically, because the largest velocities are reached in the disk. A power law radial temperature profile constructed using the highest midplane temperature at these velocities suggest that the temperature is above 20 K out to at least 75 AU, and possibly throughout the entire 125 AU disk. Radiative transfer models show that a model without CO freeze-out in the disk matches the C$^{18}$O observations better than a model with the CO snowline at $\sim$70 AU. In addition, there is no evidence for a large (order of magnitude) depletion of CO. The disk around L1527 is likely to be warm enough to have CO present in the gas phase throughout the disk, suggesting that young embedded disks can indeed be warmer than the more evolved Class II disks.

[138] arXiv:1803.04505v1 [pdf, vox]

Exploring circular polarization in the CMB due to conventional sources of cosmic birefringence

Paulo Montero-Camacho, Christopher M. Hirata
Submitted Monday 12 March 2018 @ 20:11:55 GMT
42 pages, 7 figures

The circular polarization of the cosmic microwave background (CMB) is usually taken to be zero since it is not generated by Thomson scattering. Here we explore the actual level of circular polarization in the CMB generated by conventional cosmological sources of birefringence. We consider two classes of mechanisms for birefringence. One is alignment of the matter to produce an anisotropic susceptibility tensor: the hydrogen spins can be aligned either by density perturbations or CMB anisotropies themselves. The other is anisotropy of the radiation field coupled to the non-linear response of the medium to electromagnetic fields: this can occur either via photon-photon scattering (non-linear response of the vacuum); atomic hyperpolarizability (non-linear response of neutral atoms); or plasma delay (non-linear response of free electrons). The strongest effect comes from photon-photon scattering from recombination at a level of $ \sim 10^{-14} \ \textup{K}$. Our results are consistent with a negligible circular polarization of the CMB in comparison with the linear polarization or the sensitivity of current and near-term experiments.

[139] arXiv:1803.04504v1 [pdf, vox]

Neutrino flavor transformation in supernova as a probe for nonstandard neutrino-scalar interactions

Yue Yang, James P. Kneller
Submitted Monday 12 March 2018 @ 20:09:19 GMT
27 pages, 12 figures

We explore the possibility of probing the nonstandard interactions between the neutrino and a hypothetical massive scalar or pseudoscalar via neutrino flavor transformation in supernovae. We find that in ultrarelativistic limit, the effective interaction between the neutrinos does not vanish if neutrinos are Majorana fermions but does vanish if neutrinos are Dirac fermions. The impact of the new neutrino interaction upon the flavor transformation above the neutrinosphere has been calculated in the context of the multi-angle "neutrino bulb model" and we find that the addition of the nonstandard neutrino self-interaction (NSSI) to the ordinary V-A self-interaction between neutrinos is capable of dramatically altering the collective oscillation when its strength is comparable to the standard, V-A, interaction. The effect of flavor-preserving (FP) NSSI is generally to suppress flavor transformation, while the flavor-violating (FV) components are found to promote flavor transformations. The neutrino signal from a Galactic supernova can provide complimentary constraints on scalar/pseudoscalar interactions of neutrinos as well as distinguishing whether the neutrino is a Majorana or Dirac fermion.

[140] arXiv:1803.04501v1 [pdf, vox]

Phenomenology of fermion production during axion inflation

Peter Adshead, Lauren Pearce, Marco Peloso, Michael A. Roberts, Lorenzo Sorbo
Submitted Monday 12 March 2018 @ 20:01:37 GMT
48 pages, 9 figures

We study the production of fermions through a derivative coupling with a pseudoscalar inflaton and the effects of the produced fermions on the scalar primordial perturbations. We present analytic results for the modification of the scalar power spectrum due to the produced fermions, and we estimate the amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we find a regime where the effect of the fermions gives the dominant contribution to the scalar spectrum while the amplitude of the bispectrum is small and in agreement with observation. We also note the existence of a regime in which the backreaction of the fermions on the evolution of the zero-mode of the inflaton can lead to inflation even if the potential of the inflaton is steep and does not satisfy the slow-roll conditions.

[141] arXiv:1803.04493v1 [pdf, vox]

Particle Identification In Camera Image Sensors Using Computer Vision

Miles Winter, James Bourbeau, Silvia Bravo, Felipe Campos, Matthew Meehan, Jeffrey Peacock, Tyler Ruggles, Cassidy Schneider, Ariel Levi Simons, Justin Vandenbroucke
Submitted Monday 12 March 2018 @ 19:49:18 GMT
14 pages, 14 figures, 1 table

We present a deep learning, computer vision algorithm constructed for the purposes of identifying and classifying charged particles in camera image sensors. We apply our algorithm to data collected by the Distributed Electronic Cosmic-ray Observatory (DECO), a global network of smartphones that monitors camera image sensors for the signatures of cosmic rays and other energetic particles, such as those produced by radioactive decays. The algorithm, whose core component is a convolutional neural network, achieves classification performance comparable to human quality across four distinct DECO event topologies. We apply our model to the entire DECO data set and determine a selection that achieves $\ge90\%$ purity for all event types. In particular, we estimate a purity of $98\%$ when applied to cosmic-ray muons. The automated classification is run on the public DECO data set in real time in order to provide classified particle interaction images to users of the app and other interested members of the public.

[142] arXiv:1803.04486v1 [pdf, vox]

Olivine-rich asteroids in the near-Earth space

M. Popescu, D. Perna, M. A. Barucci, S. Fornasier, A. Doressoundiram, C. Lantz, F. Merlin, I. N. Belskaya, M. Fulchignoni
Submitted Monday 12 March 2018 @ 19:39:51 GMT
10 pages, 4 figures, accepted for publication

In the framework of a 30-night spectroscopic survey of small near-Earth asteroids (NEAs) we present new results regarding the identification of olivine-rich objects. The following NEAs were classified as A-type using visible spectra obtained with 3.6 m NTT telescope: (293726) 2007 RQ17, (444584) 2006 UK, 2012 NP, 2014 YS34, 2015 HB117, 2015 LH, 2015 TB179, 2015 TW144. We determined a relative abundance of $5.4\% $ (8 out of 147 observed targets) A-types at hundred meter size range of NEAs population. The ratio is at least five times larger compared with the previously known A-types, which represent less than $\sim1\%$ of NEAs taxonomically classified. By taking into account that part of our targets may not be confirmed as olivine-rich asteroids by their near-infrared spectra, or they can have a nebular origin, our result provides an upper-limit estimation of mantle fragments at size ranges bellow 300m. Our findings are compared with the "battered-to-bits" scenario, claiming that at small sizes the olivine-rich objects should be more abundant when compared with basaltic and iron ones.

[143] arXiv:1803.04473v1 [pdf, vox]

Performance of a highly sensitive, 19-element, dual-polarization, cryogenic L-band Phased Array Feed on the Green Bank Telescope

D. Anish Roshi, W. Shillue, B. Simon, K. F. Warnick, B. Jeffs, D. J. Pisano, R. Prestage, S. White, J. R. Fisher, M. Morgan, R. Black, M. Burnett, J. Diao, M. Ruzindana, V. van Tonder, L. Hawkins, P. Marganian, T. Chamberlin, J. Ray, N. M. Pingel, K. Rajwade, D. R. Lorimer, A. Rane, J. Castro, W. Groves, L. Jensen, J. D. Nelson, T. Boyd, A. J. Beasley
Submitted Monday 12 March 2018 @ 19:21:19 GMT
24 pages, 16 figures, to appear in Astronomical Journal

A new 1.4 GHz 19-element, dual-polarization, cryogenic phased array feed (PAF) radio astronomy receiver has been developed for the Robert C. Byrd Green Bank Telescope (GBT) as part of FLAG (Focal L-band Array for the GBT) project. Commissioning observations of calibrator radio sources show that this receiver has the lowest reported beamformed system temperature ($T_{\rm sys}$) normalized by aperture efficiency ($\eta$) of any phased array receiver to date. The measured $T_{\rm sys}/\eta$ is $25.4 \pm 2.5$ K near 1350 MHz for the boresight beam, which is comparable to the performance of the current 1.4 GHz cryogenic single feed receiver on the GBT. The degradation in $T_{\rm sys}/\eta$ at $\sim$ 4 arcmin (required for Nyquist sampling) and $\sim$ 8 arcmin offsets from the boresight is, respectively, $\sim$ 1\% and $\sim$ 20\% of the boresight value. The survey speed of the PAF with seven formed beams is larger by a factor between 2.1 and 7 compared to a single beam system depending on the observing application. The measured performance, both in frequency and offset from boresight, qualitatively agree with predictions from a rigorous electromagnetic model of the PAF. The astronomical utility of the receiver is demonstrated by observations of the pulsar B0329+54 and an extended HII region, the Rosette Nebula. The enhanced survey speed with the new PAF receiver will enable the GBT to carry out exciting new science, such as more efficient observations of diffuse, extended neutral hydrogen emission from galactic in-flows and searches for Fast Radio Bursts.

[144] arXiv:1803.04470v1 [pdf, vox]

Conservative cosmology: combining data with allowance for unknown systematics

José Luis Bernal, John A. Peacock
Submitted Monday 12 March 2018 @ 19:16:51 GMT
24 pages, 8 figures

When combining data sets to perform parameter inference, the results will be unreliable if there are unknown systematics in data or models. Here we introduce a flexible methodology, BACCUS: BAyesian Conservative Constraints and Unknown Systematics, which deals in a conservative way with the problem of data combination, for any degree of tension between experiments. We introduce hyperparameters that describe a bias in each model parameter for each class of experiments. A conservative posterior for the model parameters is then obtained by marginalization both over these unknown shifts and over the width of their prior. We contrast this approach with an existing hyperparameter method in which each individual likelihood is scaled, comparing the performance of each approach and their combination in application to some idealized models. Using only these rescaling hyperparameters is not a suitable approach for the current observational situation, in which internal null tests of the errors are passed, and yet different experiments prefer models that are in poor agreement. The possible existence of large shift systematics cannot be constrained with a small number of data sets, leading to extended tails on the conservative posterior distributions. We illustrate our method with the case of the $H_0$ tension between results from the cosmic distance ladder and physical measurements that rely on the standard cosmological model.

[145] arXiv:1803.04467v1 [pdf, vox]

Witnessing Planetary Systems in the Making with the Next Generation Very Large Array

Luca Ricci, Andrea Isella, Sean M. Andrews, Tilman Birnstiel, Jeffrey N. Cuzzi, Gennaro D'Angelo, Ruobing Dong, Anne Dutrey, Barbara Ercolano, Paul R. Estrada, Mario Flock, Hui Li, Shang-Fei Liu, Wladimir Lyra, Karin Oberg, Satoshi Okuzumi, Laura Perez, Neal Turner, Nienke van der Marel, David Wilner, Andrew N. Youdin, Zhaohuan Zhu
Submitted Monday 12 March 2018 @ 19:06:31 GMT
6 pages, 3 figures, White Paper submitted to the National Academies of Science, Engineering, and Medicine's Exoplanet Science Strategy Call for Papers

The discovery of thousands of exoplanets over the last couple of decades has shown that the birth of planets is a very efficient process in nature. Theories invoke a multitude of mechanisms to describe the assembly of planets in the disks around pre-main-sequence stars, but observational constraints have been sparse on account of insufficient sensitivity and resolution. Understanding how planets form and interact with their parental disk is crucial also to illuminate the main characteristics of a large portion of the full population of planets that is inaccessible to current and near-future observations. This White Paper describes some of the main issues for our current understanding of the formation and evolution of planets, and the critical contribution expected in this field by the Next Generation Very Large Array.

[146] arXiv:1803.04461v1 [pdf, vox]

Chemical Abundances of Main-Sequence, Turn-off, Subgiant and red giant Stars from APOGEE spectra I: Signatures of Diffusion in the Open Cluster M67

Diogo Souto, Katia Cunha, Verne V. Smith, C. Allende Prieto, D. A. Garcia-Hernandez, Marc Pinsonneault, Parker Holzer, Peter Frinchaboy, Jon Holtzman, J. A. Johnson, Henrik Jonsson, Steven R. Majewski, Matthew Shetrone, Jennifer Sobeck, Guy Stringfellow, Johanna Teske, Olga Zamora, Gail Zasowski, Ricardo Carrera, Keivan Stassun, J. G. Fernandez-Trincado, Sandro Villanova, Dante Minniti, Felipe Santana
Submitted Monday 12 March 2018 @ 18:59:39 GMT
Accepted to ApJ

Detailed chemical abundance distributions for fourteen elements are derived for eight high-probability stellar members of the solar metallicity old open cluster M67 with an age of $\sim$4 Gyr. The eight stars consist of four pairs, with each pair occupying a distinct phase of stellar evolution: two G-dwarfs, two turnoff stars, two G-subgiants, and two red clump K-giants. The abundance analysis uses near-IR high-resolution spectra ($\lambda$1.5 -- 1.7$\mu$m) from the APOGEE survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for 2M08510076+113115 suggest that this star is a solar-twin, exhibiting abundance differences relative to the Sun of $\leq$ 0.04 dex for all elements. Chemical homogeneity is found within each class of stars ($\sim$0.02 dex), while significant abundance variations ($\sim$0.05 -- 0.20 dex) are found across the different evolutionary phases; the turnoff stars typically have the lowest abundances, while the red clump tend to have the largest. Non-LTE corrections to the LTE-derived abundances are unlikely to explain the differences. A detailed comparison of the derived Fe, Mg, Si, and Ca abundances with recently published surface abundances from stellar models that include chemical diffusion, provides a good match between the observed and predicted abundances as a function of stellar mass. Such agreement would indicate the detection of chemical diffusion processes in the stellar members of M67.

[147] arXiv:1803.04457v1 [pdf, vox]

Key Technology Challenges for the Study of Exoplanets and the Search for Habitable Worlds

Brendan Crill, Nick Siegler, Shawn Domagal-Goldman, Eric Mamajek, Karl Stapelfeldt
Submitted Monday 12 March 2018 @ 18:54:38 GMT
arXiv admin note: substantial text overlap with arXiv:1801.07811

In support of the National Acadamies' Exoplanet Science Strategy, this whitepaper outlines key technology challenges for studying the diversity of worlds in the Galaxy and in searching for habitable planets. Observations of habitable planets outside of our solar system require technologies enabling the measurement of (1) spectral signatures of gases in their atmospheres, some of which may be of biological origin, and (2) planetary mass. Technology gaps must be closed in many areas. In some cases, performance requirements are 1-2 orders of magnitude from the current state-of-the-art. Thes technology gaps are in the areas of: starlight suppression (for reflection or emission spectroscopy; coronagraphs or starshades, contrast stability, detector sensitivity, collecting area, spectroscopic sensitivity, radial stellar motion sensitivity, and tangential stellar motion sensitivity. The technologies advancing to close these gaps are identified through the NASA Exoplanet Exploration Program's (ExEP's) annual Technology Selection and Prioritization Process in collaboration with the larger exoplanet science and technology communities. Details can be found in the annual ExEP Technology Plan Appendix. Looking towards the more distant future, the size of a desired single-aperture space telescope, even when folded, may exceed current launch capabilities, suggesting the study of in-space assembly approaches. Additionally, mid-infrared spectral observations of candidate habitable worlds may be needed to rule out false positives observed at shorter wavelengths and add supportive evidence. Consequently, single aperture telescopes may prove impractically large and space interferometry may be needed, as identified in NASA's 30 year roadmap Enduring Quests, Daring Visions

[148] arXiv:1803.05312v1 [pdf, vox]

Second Order Perturbative Effects on the Acoustic Geometry

Nandan Roy, Shivani Singh, Sankhasubhra Nag, Tapas K. Das
Submitted Monday 12 March 2018 @ 18:49:22 GMT
Latex 2e, 9 pages

In this work, we have studied the effect of higher order perturbations, particularly the second order in details, on the sonic horizon. We have considered two different schemes of perturbations which are velocity potential perturbation and mass acceleration rate perturbation. These two schemes give us qualitatively similar behaviour. We have found that the analogue gravity formalism also holds for the higher order perturbations.

[149] arXiv:1803.04446v1 [pdf, vox]

Magnetic bipoles in rotating turbulence with coronal envelope

I. R. Losada, J. Warnecke, A. Brandenburg, N. Kleeorin, I. Rogachevskii
Submitted Monday 12 March 2018 @ 18:29:20 GMT
14 pages, 20 figures, submitted to A&A

The formation of sunspots and starspots is not yet fully understood and is therefore one of the major open problems in solar and stellar physics. Magnetic flux concentrations can be produced by the negative effective magnetic pressure instability (NEMPI). This instability is strongly suppressed by rotation. However, the presence of an outer coronal envelope was previously found to strengthen the flux concentrations and make them more prominent. It also allows for the formation of bipolar regions (BRs). We want to know whether the presence of an outer coronal envelope also changes the excitation conditions and the rotational dependence of NEMPI. We use direct numerical simulations and mean-field simulations. We adopt a simple two-layer model of turbulence that mimics the jump between the convective turbulent and coronal layers below and above the surface of a star, respectively. The computational domain is Cartesian and located at a certain latitude of a rotating sphere. We investigate the effects of rotation on NEMPI by changing the Coriolis number, the latitude, and the box resolution. Rotation has a strong impact on the process of BR formation. Even rather slow rotation is found to suppress their formation. However, increasing the imposed magnetic field strength also makes the structures stronger and alleviates the rotational suppression somewhat. The presence of a coronal layer itself does not significantly alleviate the effects of rotational suppression.

[150] arXiv:1803.04445v1 [pdf, vox]

Manufacturing cosmic rays in the evolving dynamical states of galaxy clusters

Reju Sam John, Surajit Paul, Luigi Iapichino, Karl Mannheim, Harish Kumar
Submitted Monday 12 March 2018 @ 18:29:08 GMT
Submitted to MNRAS

Galaxy clusters are known to be the reservoirs of Cosmic Rays (CRs), mostly inferred from theoretical calculations or detection of CR derived observables. Though CR electrons have been detected through radio emissions, CR protons and its derivative gamma rays remained undetected. CR acceleration in clusters is mostly attributed to its dynamical activities that produce shocks. Shocks in clusters emerge out of merger or accretion but, which one is more effective? at which dynamical phase? and why? So, in quest of answers, we study the detail evolution of cosmic ray emission in the galaxy clusters using cosmological simulations with {\sc enzo} code. Defining appropriate dynamical states using the concept of virialization, we have studied a sample of merging and non-merging clusters. We report that the merger shocks (Mach, $\mathcal{M}=2-5$) are the most effective CR producers in clusters. Clusters once merged, permanently deviate from CR and X-ray mass scaling of non-merging systems, enabling us to use it as a tool to determine the state of merger. Through a temporal and spatial evolution study, we found a strong correlation between cluster merger dynamics and CR production. We have observed that the brightest phase of X-ray and CR emission from clusters occur respectively about 1.0 and 1.5 Gyr after every merger. This significant finding of non concurrent appearance of X-ray and CR emission peaks can explain the non-detection of gamma-rays from many X-ray bright galaxy clusters. This can also be a guiding information to select appropriate targets for gamma-ray detection from clusters.

[151] arXiv:1803.04440v1 [pdf, vox]

Rotation of Low-Mass Stars in Upper Scorpius and Rho Ophiuchus with K2

L. M. Rebull, J. R. Stuaffer, A. M. Cody, L. A. Hillenbrand, T. J. David, M. Pinsonneault
Submitted Monday 12 March 2018 @ 18:24:33 GMT
Accepted by AJ

We present an analysis of K2 light curves (LCs) for candidate members of the young Upper Sco (USco) association $\sim$8 Myr) and the neighboring Rho Oph embedded cluster ($\sim$1 Myr). We establish $\sim$1300 stars as probable members, $\sim$80\% of which are periodic. The phased LCs have a variety of shapes which can be attributed to physical causes ranging from stellar pulsation and stellar rotation to disk-related phenomena. We identify and discuss a number of observed behaviors. The periods are $\sim$0.2-30 days with a peak near 2 days and the rapid period end nearing break-up velocity. M stars in the young USco region rotate systematically faster than GK stars, a pattern also present in K2 data for the older Pleiades and Praesepe systems. At higher masses (types FGK), the well-defined period-color relationship for slowly rotating stars seen in the Pleiades and Praesepe is not yet present in USco. Circumstellar disks are present predominantly among the more slowly rotating Ms in USco, with few disks in the sub-day rotators. However, M dwarfs with disks rotate faster on average than FGK systems with disks. For four of these disked Ms, we provide direct evidence for disk-locking based on the K2 LC morphologies. Our preliminary analysis shows a relatively mass-independent spin-up by a factor of $\sim$3.5 between USco and the Pleiades, then mass-dependent spin-down between Pleiades and Praesepe.

[152] arXiv:1803.04437v1 [pdf, vox]

Spitzer Opens New Path to Break Classic Degeneracy for Jupiter-Mass Microlensing Planet OGLE-2017-BLG-1140Lb

S. Calchi Novati, J. Skowron, Y. K. Jung, C. Beichman, G. Bryden, S. Carey, B. S. Gaudi, C. B. Henderson, Y. Shvartzvald, J. C. Yee, W. Zhu, A. Udalski, M. K. Szymański, P. Mróz, R. Poleski, I. Soszyński, S. Kozłowski, P. Pietrukowicz, K. Ulaczyk, M. Pawlak, K. Rybicki, P. Iwanek, M. D. Albrow, S. -J. Chung, A. Gould, C. Han, K. -H. Hwang, Y. -H. Ryu, I. -G. Shin, W. Zang, S. -M. Cha, D. -J. Kim, H. -W. Kim, S. -L. Kim, C. -U. Lee, D. -J. Lee, Y. Lee, B. -G. Park, R. W. Pogge
Submitted Monday 12 March 2018 @ 18:12:45 GMT
Submitted to AAS

We analyze the combined Spitzer and ground-based data for OGLE-2017-BLG-1140 and show that the event was generated by a Jupiter-class $(m_p\simeq 1.6\,M_{\rm jup})$ planet orbiting a mid-late M dwarf $(M\simeq 0.2\,M_\odot)$ that lies $D_{LS}\simeq 1.0\,\mathrm{kpc}$ in the foreground of the microlensed, Galactic-bar, source star. The planet-host projected separation is $a_\perp \simeq 1.0\,\mathrm{au}$, i.e., well-beyond the snow line. By measuring the source proper motion ${\mathbf{\mu}}_s$ from ongoing, long-term OGLE imaging, and combining this with the lens-source relative proper motion ${\mathbf{\mu}}_\mat​hrm{rel}$ derived from the microlensing solution, we show that the lens proper motion ${\mathbf{\mu}}_l={\​mathbf{\mu}}_\mathrm​{rel} + {\mathbf{\mu}}_s$ is consistent with the lens lying in the Galactic disk. We show that while the Spitzer and ground-based data are comparably well fitted by planetary (i.e., binary-lens, 2L1S) models and by binary-source (1L2S) models, the combination of Spitzer and ground-based data decisively favor the planetary model. This is a new channel to resolve the 2L1S/1L2S degeneracy, which can be difficult to break in some cases.

[153] arXiv:1803.04436v1 [pdf, vox]

Modelling the early time behaviour of type Ia supernovae: effects of the $^{56}$Ni distribution

M. R. Magee, S. A. Sim, R. Kotak, W. E. Kerzendorf
Submitted Monday 12 March 2018 @ 18:11:20 GMT
14 pages, 8 figures, 2 tables. Accepted for publication in Astronomy & Astrophysics

Recent studies have demonstrated the diversity in type Ia supernovae (SNe Ia) at early times and highlighted a need for a better understanding of the explosion physics as manifested by observations soon after explosion. To this end, we present a Monte Carlo code designed to model the light curves of radioactively driven, hydrogen-free transients from explosion to approximately maximum light. In this initial study, we have used a parametrised description of the ejecta in SNe Ia, and performed a parameter study of the effects of the $^{56}$Ni distribution on the observed colours and light curves for a fixed $^{56}$Ni mass of 0.6 $M_\odot$. For a given density profile, we find that models with $^{56}$Ni extending throughout the entirety of the ejecta are typically brighter and bluer shortly after explosion. Additionally, the shape of the density profile itself also plays an important role in determining the shape, rise time, and colours of observed light curves. We find that the multi-band light curves of at least one SNe Ia (SN 2009ig) are inconsistent with less extended $^{56}$Ni distributions, but show good agreement with models that incorporate $^{56}$Ni throughout the entire ejecta. We further demonstrate that comparisons with full $UVOIR$ colour light curves are powerful tools in discriminating various $^{56}$Ni distributions, and hence explosion models.

[154] arXiv:1803.04427v1 [pdf, vox]

Particle-in-cell simulations of pair discharges in a starved magnetosphere of a Kerr black hole

Amir Levinson, Benoît Cerutti
Submitted Monday 12 March 2018 @ 18:00:30 GMT
14 pages, 6 figures, Submitted to Astronomy & Astrophysics

We investigate the dynamics and emission of a starved magnetospheric region (gap) formed in the vicinity of a Kerr black hole horizon, using a new, fully general relativistic particle-in-cell code that implements Monte-Carlo methods to compute gamma-ray emission and pair production through the interaction of pairs and gamma rays with soft photons emitted by the accretion flow. It is found that when the Thomson length for collision with disk photons exceeds the gap width, screening of the gap occurs through low amplitude, rapid plasma oscillations that produce self-sustained pair cascades, with quasi-stationary pair and gamma-ray spectra, and with a pair multiplicity that increases in proportion to the pair production opacity. The gamma ray spectrum emitted from the gap peaks in the TeV band, with a total luminosity that constitutes a fraction of about $10^{-5}$ of the corresponding Blandford-Znajek power. This stage is preceded by a prompt discharge phase of duration $\sim r_g/c$, during which the potential energy initially stored in the gap is released as a flare of curvature TeV photons. We speculate that the TeV emission observed in M87 may be produced by pair discharges in a spark gap.

[155] arXiv:1803.04425v1 [pdf, vox]

Stellar and nebular diagnostics in the UV for star-forming galaxies

Nell Byler, Julianne Dalcanton, Charlie Conroy, Benjamin Johnson, Emily Levesque, Danielle Berg
Submitted Monday 12 March 2018 @ 18:00:15 GMT
34 pages, 20 figures, plus appendix

There is a long history of using optical emission and absorption lines to constrain the metallicity and ionization parameters of gas in galaxies. However, comparable diagnostics are less well-developed for the UV. Here,} we assess the diagnostic potential of both absorption and emission features in the UV and evaluate the diagnostics against observations of local and high redshift galaxies. We use the {\tt CloudyFSPS} nebular emission model of Byler+2017, extended to include emission predictions in the UV, to evaluate the metallicity sensitivity of established UV stellar absorption indices, and to identify those that include a significant contribution from nebular emission. We present model UV emission line fluxes as a function of metallicity and ionization parameter, assuming both instantaneous bursts and constant SFRs. We identify combinations of strong emission lines that constrain metallicity and ionization parameter, including [CIII]$\lambda1907$, CIII]$\lambda1909$, OIII]$\lambda1661,16​66$, SiIII]$\lambda1883,1​892$, CIV$\lambda$1548,155​1, NII]$\lambda1750,175​2$, and MgII$\lambda2796$, and develop UV versions of the canonical "BPT" diagram. We quantify the relative contribution from stellar wind emission and nebular line emission to diagnostic line ratios that include the CIV$\lambda$1548,155​1 lines, and also develop an observationally motivated relationship for N and C enrichment that improves the performance of photoionization models. We summarize the best diagnostic choices and the associated redshift range for low-, mid-, and high-resolution rest-UV spectroscopy in preparation for the launch of JWST.

[156] arXiv:1803.04424v1 [pdf, vox]

Evidence for Pulsar-like Emission Components in the Broadband ULX Sample

D. J. Walton, F. Fuerst, M. Heida, F. A. Harrison, D. Barret, D. Stern, M. Bachetti, M. Brightman, A. C. Fabian, M. J. Middleton
Submitted Monday 12 March 2018 @ 18:00:09 GMT
13 pages, 6 figures; accepted for publication in ApJ

We present broadband X-ray analyses of a sample of bright ultraluminous X-ray sources with the goal of investigating the spectral similarity of this population to the known ULX pulsars, M82 X-2, NGC7793 P13 and NGC5907 ULX. We perform a phase-resolved analysis of the broadband XMM-Newton+NuSTAR dataset of NGC5907 ULX, finding that the pulsed emission from the accretion column in this source exhibits a similar spectral shape to that seen in both M82 X-2 and NGC7793 P13, and that this is responsible for the excess emission observed at the highest energies when the spectra are fit with accretion disk models. We then demonstrate that similar 'hard' excesses are seen in all the ULXs in the broadband sample. Finally, for the ULXs where the nature of the accretor is currently unknown, we test whether the hard excesses are all consistent with being produced by an accretion column similar to those present in M82 X-2, NGC7793 P13 and NGC5907 ULX. Based on the average shape of the pulsed emission, we find that in all cases a similar accretion column can successfully reproduce the observed data, consistent with the hypothesis that this ULX sample may be dominated by neutron star accretors. Compared to the known pulsar ULXs, our spectral fits for the remaining ULXs suggest that the non-pulsed emission from the accretion flow beyond the magnetosphere makes a stronger relative contribution than the component associated with the accretion column. If these sources do also contain neutron star accretors, this may help to explain the lack of detected pulsations.

[157] arXiv:1803.04421v1 [pdf, vox]

The rate of Type-Ia supernovae in galaxy clusters out to redshift 1.75

Matan Friedmann, Dan Maoz
Submitted Monday 12 March 2018 @ 18:00:02 GMT
MNRAS, submitted

The delay-time distribution (DTD) of Type-Ia supernovae (SNe-Ia) is a valuable probe of SN Ia progenitors and physics. The SN-Ia rate in galaxy clusters as a function of cluster redshift is an almost-direct measure of the DTD, but current estimates have been limited out to a mean redshift z=1.1, corresponding to time delays, after cluster star-formation, of >3.2 Gyr. We analyze data from a Hubble Space Telescope monitoring project of 12 galaxy clusters at z=1.13-1.75, where we discover 29 SN candidates, and present their multi-band light curves. Based on the SN photometry and the apparent host galaxies, we estimate that 9 cases are likely SNe-Ia in cluster galaxies and 6 more are possible, but not certain, cluster SNe-Ia. We simulate the SN detection efficiency and completeness, and perform photometry of the cluster galaxies to derive the cluster stellar masses. With this input, we obtain a mean z=1.35 cluster SN-Ia rate per unit formed stellar mass of R=2.4(+3.4-1.6)e-13/​yr/Msun. Separating into low-z (z=1.25) and high-z (z=1.58) bins, the rates are R=1.9(+2.8-1.4)e-13/​yr/Msun, and R=3.5(+6.6-2.8)e-13/​yr/Msun. Together with previously measured cluster SN-Ia rates, we fit the DTD, now down to delays of 1.5 Gyr, with a power-law dependence, t^alpha, and find alpha=-1.30(+0.24-0.​15). We confirm previous indications for a SN Ia production efficiency several times higher in galaxy clusters than in the field, perhaps caused by a peculiar stellar initial mass function in clusters, or by a higher incidence of tight binaries.

[158] arXiv:1803.04422v1 [pdf, vox]

SHINING, A Survey of Far Infrared Lines in Nearby Galaxies. II: Line-Deficit Models, AGN impact, [CII]-SFR Scaling Relations, and Mass-Metallicity Relation in (U)LIRGS

R. Herrera-Camus, E. Sturm, J. Graciá-Carpio, D. Lutz, A. Contursi, S. Veilleux, J. Fischer, E. González-Alfonso, A. Poglitsch, L. Tacconi, R. Genzel, R. Maiolino, A. Sternberg, R. Davies, A. Verma
Submitted Monday 12 March 2018 @ 18:00:02 GMT
22 pages, 7 Figures, Accepted for publication in the Astrophysical Journal

The SHINING survey (Paper I; Herrera-Camus et al. 2018) offers a great opportunity to study the properties of the ionized and neutral media of galaxies from prototypical starbursts and active galactic nuclei (AGN) to heavily obscured objects. Based on Herschel/PACS observations of the main far-infrared (FIR) fine-structure lines, in this paper we analyze the physical mechanisms behind the observed line deficits in galaxies, the apparent offset of luminous infrared galaxies (LIRGs) from the mass-metallicity relation, and the scaling relations between [CII] 158 $\mu$m line emission and star formation rate (SFR). Based on a toy model and the Cloudy code, we conclude that the increase in the ionization parameter with FIR surface brightness can explain the observed decrease in the line-to-FIR continuum ratio of galaxies. In the case of the [CII] line, the increase in the ionization parameter is accompanied by a reduction in the photoelectric heating efficiency and the inability of the line to track the increase in the FUV radiation field as galaxies become more compact and luminous. In the central $\sim$kiloparsec regions of AGN galaxies we observe a significant increase in the [OI] 63 $\mu$m/[CII] line ratio; the AGN impact on the line-to-FIR ratios fades on global scales. Based on extinction-insensiti​ve metallicity measurements of LIRGs we confirm that they lie below the mass-metallicity relation, but the offset is smaller than those reported in studies that use optical-based metal abundances. Finally, we present scaling relations between [CII] emission and SFR in the context of the main-sequence of star-forming galaxies.

[159] arXiv:1803.04417v1 [pdf, vox]

The Maximum Mass Solar Nebula and the early formation of planets

C. J. Nixon, A. R. King, J. E. Pringle
Submitted Monday 12 March 2018 @ 18:00:01 GMT
6 pages, no figures, accepted for publication in MNRAS

Current planet formation theories provide successful frameworks with which to interpret the array of new observational data in this field. However, each of the two main theories (core accretion, gravitational instability) is unable to explain some key aspects. In many planet formation calculations, it is usual to treat the initial properties of the planet forming disc (mass, radius, etc.) as free parameters. In this paper, we stress the importance of setting the formation of planet forming discs within the context of the formation of the central stars. By exploring the early stages of disc formation, we introduce the concept of the Maximum Mass Solar Nebula (MMSN), as opposed to the oft-used Minimum Mass Solar Nebula (here mmsn). It is evident that almost all protoplanetary discs start their evolution in a strongly self-gravitating state. In agreement with almost all previous work in this area, we conclude that on the scales relevant to planet formation these discs are not gravitationally unstable to gas fragmentation, but instead form strong, transient spiral arms. These spiral arms can act as efficient dust traps allowing the accumulation and subsequent fragmentation of the dust (but not the gas). This phase is likely to populate the disc with relatively large planetesimals on short timescales while the disc is still veiled by a dusty-gas envelope. Crucially, the early formation of large planetesimals overcomes the main barriers remaining within the core accretion model. A prediction of this picture is that essentially all observable protoplanetary discs are already planet hosting.

[160] arXiv:1803.04419v1 [pdf, vox]

SHINING, A Survey of Far Infrared Lines in Nearby Galaxies. I: Survey Description, Observational Trends, and Line Diagnostics

R. Herrera-Camus, E. Sturm, J. Graciá-Carpio, D. Lutz, A. Contursi, S. Veilleux, J. Fischer, E. González-Alfonso, A. Poglitsch, L. Tacconi, R. Genzel, R. Maiolino, A. Sternberg, R. Davies, A. Verma
Submitted Monday 12 March 2018 @ 18:00:01 GMT
30 pages, 13 Figures, Accepted for publication in the Astrophysical Journal

We use the Herschel/PACS spectrometer to study the global and spatially resolved far-infrared (FIR) fine-structure line emission in a sample of 52 galaxies that constitute the SHINING survey. These galaxies include star-forming, active-galactic nuclei (AGN), and luminous infrared galaxies (LIRGs). We find an increasing number of galaxies (and kiloparsec size regions within galaxies) with low line-to-FIR continuum ratios as a function of increasing FIR luminosity ($L_{\mathrm{FIR}}$)​, dust infrared color, $L_{\mathrm{FIR}}$ to molecular gas mass ratio ($L_{\mathrm{FIR}}/M​_{\mathrm{mol}}$), and FIR surface brightness ($\Sigma_{\mathrm{FI​R}}$). The correlations between the [CII]/FIR or [OI]/FIR ratios with $\Sigma_{\mathrm{FIR​}}$ are remarkably tight ($\sim0.3$ dex scatter over almost four orders of magnitude in $\Sigma_{\mathrm{FIR​}}$). We observe that galaxies with $L_{\mathrm{FIR}}/M_​{\mathrm{mol}} \gtrsim 80\,L_{\odot}\,M_{\o​dot}^{-1}$ and $\Sigma_{\mathrm{FIR​}}\gtrsim10^{11}$ $L_{\odot}$ kpc$^{-2}$ tend to have weak fine-structure line-to-FIR continuum ratios, and that LIRGs with infrared sizes $\gtrsim1$ kpc have line-to-FIR ratios comparable to those observed in typical star-forming galaxies. We analyze the physical mechanisms driving these trends in Paper II (Herrera-Camus et al. 2018). The combined analysis of the [CII], [NII], and [OIII] lines reveals that the fraction of the [CII] line emission that arises from neutral gas increases from 60% to 90% in the most active star-forming regions and that the emission originating in the ionized gas is associated with low-ionization, diffuse gas rather than with dense gas in HII regions. Finally, we report the global and spatially resolved line fluxes of the SHINING galaxies to enable the comparison and planning of future local and high-$z$ studies.

[161] arXiv:1803.04412v1 [pdf, vox]

Quantum Standard Clocks in the Primordial Trispectrum

Xingang Chen, Wan Zhen Chua, Yuxun Guo, Yi Wang, Zhong-Zhi Xianyu, Tianyou Xie
Submitted Monday 12 March 2018 @ 18:00:00 GMT
23 pages

We calculate the primordial trispectrum of curvature perturbation in quasi-single field inflation, with general sound speeds for both the inflaton and the massive scalar. Special attention is paid to various soft limits of the trispectrum, where the shape function shows characteristic oscillatory pattern (known as the quantum primordial standard clock signal) as a function of the momentum ratio. Our calculation is greatly simplified by using the "mixed propagator" developed under a diagrammatic representation of the in-in formalism.

[162] arXiv:1803.04415v1 [pdf, vox]

Chromospheric counterparts of solar transition region unresolved fine structure loops

Tiago M. D. Pereira, Luc Rouppe van der Voort, Viggo H. Hansteen, Bart De Pontieu
Submitted Monday 12 March 2018 @ 18:00:00 GMT
5 pages, 3 figures, 2 movies; accepted for publication in A&A Letters

Low-lying loops have been discovered at the solar limb in transition region temperatures by the Interface Region Imaging Spectrograph (IRIS). They do not appear to reach coronal temperatures, and it has been suggested that they are the long-predicted unresolved fine structures (UFS). These loops are dynamic and believed to be visible during both heating and cooling phases. Making use of coordinated observations between IRIS and the Swedish 1-m Solar Telescope, we study how these loops impact the solar chromosphere. We show for the first time that there is indeed a chromospheric signal of these loops, seen mostly in the form of strong Doppler shifts and a conspicuous lack of chromospheric heating. In addition, we find that several instances have a inverse Y-shaped jet just above the loop, suggesting that magnetic reconnection is driving these events. Our observations add several puzzling details to the current knowledge of these newly discovered structures; this new information must be considered in theoretical models.

[163] arXiv:1803.04381v1 [pdf, vox]

Convection Enhances Magnetic Turbulence in AM CVn Accretion Disks

Matthew S. B. Coleman, Omer Blaes, Shigenobu Hirose, Peter H. Hauschildt
Submitted Monday 12 March 2018 @ 17:18:37 GMT
15 pages, 10 figures, accepted for publication in ApJ

We present the results of local, vertically stratified, radiation magnetohydrodynamic shearing box simulations of magnetorotational instability (MRI) turbulence for a (hydrogen poor) composition applicable to accretion disks in AM CVn type systems. Many of these accreting white dwarf systems are helium analogues of dwarf novae (DNe). We utilize frequency-integrated opacity and equation of state tables appropriate for this regime to accurately portray the relevant thermodynamics. We find bistability of thermal equilibria in the effective temperature, surface mass density plane typically associated with disk instabilities. Along this equilibrium curve (i.e. the S-curve) we find that the stress to thermal pressure ratio $\alpha$ varied with peak values of $\sim 0.15$ near the tip of the upper branch. Similar to DNe, we found enhancement of $\alpha$ near the tip of the upper branch caused by convection; this increase in $\alpha$ occurred despite our choice of zero net vertical magnetic flux. Two notable differences we find between DN and AM CVn accretion disk simulations are that AM CVn disks are capable of exhibiting persistent convection in outburst, and ideal MHD is valid throughout quiescence for AM CVns. In contrast, DNe simulations only show intermittent convection, and non-ideal MHD effects are likely important in quiescence. By combining our previous work with these new results, we also find that convective enhancement of the MRI is anticorrelated with mean molecular weight.

[164] arXiv:1803.04370v1 [pdf, vox]

Galactic Binaries Can Explain the Fermi Galactic Center Excess and 511 keV Emission

Richard Bartels, Francesca Calore, Emma Storm, Christoph Weniger
Submitted Monday 12 March 2018 @ 16:55:07 GMT
11 pages, 5 figures, appendix, comments welcome

The Fermi-LAT Galactic Center excess and the 511 keV positron-annihilatio​n signal from the inner Galaxy bare a striking morphological similarity. We propose that both can be explained through a scenario in which millisecond pulsars produce the Galactic Center excess and their progenitors, low-mass X-ray binaries, the 511 keV signal. As a proof-of-principle we study a specific population synthesis scenario from the literature involving so-called ultracompact X-ray binaries. Moreover, for the first time, we quantitatively show that neutron star, rather than black hole, low-mass X-ray binaries can be responsible for the majority of the positrons. In this particular scenario binary millisecond pulsars can be both the source of the Fermi-LAT $\gamma$-ray excess and the bulge positrons. Future avenues to test this scenario are discussed.

[165] arXiv:1803.04356v1 [pdf, vox]

SPH simulations of the induced gravitational collapse scenario of long gamma-ray bursts associated with supernovae

L. Becerra, C. L. Ellinger, C. L. Fryer, J. A. Rueda, R. Ruffini
Submitted Monday 12 March 2018 @ 16:24:28 GMT
Submitted to The Astrophysical Journal

We present the first three-dimensional (3D) smoothed-particle-hy​drodynamics (SPH) simulations of the induced gravitational collapse (IGC) scenario of long-duration gamma-ray bursts (GRBs) associated with supernovae (SNe). We simulate the SN explosion of a carbon-oxygen core (CO$_{\rm core}$) forming a binary system with a neutron star (NS) companion. We follow the evolution of the SN ejecta, including their morphological structure, subjected to the gravitational field of both the new NS ($\nu$NS) formed at the center of the SN, and the one of the NS companion. We compute the accretion rate of the SN ejecta onto the NS companion as well as onto the $\nu$NS from SN matter fallback. We determine the fate of the binary system for a wide parameter space including different CO$_{\rm core}$ masses, orbital periods and SN explosion geometry and energies. We evaluate, for selected nuclear equations-of-state of NSs, if the accretion process leads the NSs either to the mass-shedding limit, or to the secular axisymmetric instability for gravitational collapse to a black hole (BH), or to a more massive, fast rotating, but stable NS. We also assess whether the binary keeps or not gravitationally bound after the SN explosion, hence exploring the space of binary and SN explosion parameters leading to the formation of $\nu$NS-NS or $\nu$NS-BH binaries. The consequences of our results for the modeling of GRBs via the IGC scenario are discussed.

[166] arXiv:1803.04338v1 [pdf, vox]

Flickering in AGB stars: Probing the nature of accreting companions

S. Snaid, A A. Zijlstra, I. McDonald, Helen Barker, T. R. Marsh, V. S. Dhillon
Submitted Monday 12 March 2018 @ 16:05:30 GMT

Binary companions to asymptotic giant branch (AGB) stars are an important aspect of their evolution. Few AGB companions have been detected, and in most cases it is difficult to distinguish between main-sequence and white dwarf companions. Detection of photometric flickering, a tracer of compact accretion disks around white dwarfs, can help identify the nature of these companions. In this work, we searched for flickering in four AGB stars suggested to have likely accreting companions. We found no signs for flickering in two targets: R~Aqr and V1016 Cyg. Flickering was detected in the other two stars: Mira and Y Gem. We investigated the true nature of Mira's companion using three different approaches. Our results for Mira strongly suggest that its companion is a white dwarf.

[167] arXiv:1803.04335v1 [pdf, vox]

A unified accretion-ejection paradigm for black hole X-ray binaries. II. Observational signatures of Jet Emitting Disks

G. Marcel, J. Ferreira, P-O. Petrucci, G. Henri, R. Belmont, M. Clavel, J. Malzac, M. Coriat, S. Corbel, J. Rodriguez, A. Loh, S. Chakravorty, S. Drappeau
Submitted Monday 12 March 2018 @ 16:03:27 GMT
Accepted for publication in A&A

We elaborate on the paradigm proposed in Ferreira et al. (2006). For $\mu>0.1$, the accretion flow produces jets that vertically, carry away the disk angular momentum (Jet Emitting Disk or JED). The goal of this paper is to investigate the spectral signatures of the JED configurations. We have developed a two-temperature plasma code that computes the disk local thermal equilibria, taking into account the advection of energy in an iterative way. Our code addresses optically thin/thick transitions, both radiation and gas supported regimes and computes in a consistent way the emitted spectrum from a steady-state disk. The optically thin emission is obtained using the BELM code, which provides accurate spectra for Bremsstrahlung and Synchrotron emission processes as well as for their local Comptonisation. For a range in radius and accretion rates, JEDs exhibit three thermal equilibria, one thermally unstable and two stable. Due to the existence of two thermally stable solutions, an hysteresis cycle is naturally obtained. However, standard outbursting X-ray binary cycles cannot be reproduced. Another striking feature of JEDs is their ability to reproduce luminous Hard States. At high accretion rates JEDs become slim, where the main cooling is advection. When the loss of angular momentum and power in jets is then consistently taken into account, accretion disks have spectral signatures that are consistent with Hard states, up to large luminosities. The reproduction of Soft states being well performed by Standard Accretion Disks (SAD), this study advocates for the existence of hybrid disk configuration: JED and SAD. A study of such hybrid configuration will be presented in a forthcoming paper III.

[168] arXiv:1803.04330v1 [pdf, vox]

A Uniformly Selected Sample of Low-Mass Black Holes in Seyfert 1 Galaxies. II. The SDSS DR7 Sample

He-Yang Liu, Weimin Yuan, Xiao-Bo Dong, Hongyan Zhou, Wen-Juan Liu
Submitted Monday 12 March 2018 @ 15:59:30 GMT
50 pages, 16 figures, submitted to ApJS

A new sample of 204 low-mass black holes (LMBHs) in active galactic nuclei (AGNs) is presented with black hole masses in the range of $(1-20) \times 10^5 M_{\odot}$. The AGNs are selected from a systematic search among galaxies in the Data Release (DR) 7 of the Sloan Digital Sky Survey (SDSS), by careful analyses of their optical spectra and precise measurement of spectral parameters. Combining them with our previous sample selected from the SDSS DR 4 (Dong et al. 2012) makes it the largest LMBH sample so far, totaling over 500 objects. Some of the statistical properties of the combined LMBH AGN sample are briefly discussed, in the context of exploring the low-mass end of the AGN population. Their X-ray luminosities follow the extension of the previously known correlation with the $ {\rm [O\,{\tiny III}]}$ luminosity. The effective optical-to-X-ray spectral indices $\rm \alpha_{OX}$, albeit a large scatter, are broadly consistent with the extension of the relation with the near-UV luminosity $L_{\rm 2500 \AA}$. Interestingly, a correlation of $\rm \alpha_{OX}$ with black hole mass is also found in the sense that $\rm \alpha_{OX}$ is statistically flatter (stronger X-ray relative to optical) for lower black hole mass. Only 26 objects, mostly radio loud, were detected in radio at 20 cm in the FIRST survey, making a radio loud fraction of 4%. The host galaxies of LMBHs have stellar masses in the range of $10^{8.8-12.4} M_{\odot}$ and optical colors typical of Sbc spirals. They are dominated by young stellar populations which seem to have undergone a continuous star formation history.

[169] arXiv:1803.04323v1 [pdf, vox]

The formation of astrophysical Mg-rich silicate dust

Christopher Mauney, Davide Lazzati
Submitted Monday 12 March 2018 @ 15:51:06 GMT
21 pages, submitted to Molecular Astrophysics

We present new results for ground-state candidate energies of Mg-rich olivine (MRO) clusters and use the binding energies of these clusters to determine their nucleation rates in stellar outflows, with particular interest in the en- vironments of core-collapse supernovae (CCSNe). Low-lying structures of clusters (Mg2SiO4)n 2 \le n \le 13 are determined from a modified minima hopping algorithm using an empirical silicate potential in the Buckingham form. These configurations are further refined and optimized using the den- sity functional theory code Quantum Espresso. Utilizing atomistic nucleation theory, we determine the critical size and nucleation rates of these clusters. We find that configurations and binding energies in this regime are very dis- similar from those of the bulk lattice. Clusters grow with SiO_4-MgO layering and exhibit only global, rather than local, symmetries. When compared to classical nucleation theory we find suppressed nucleation rates at most temperatures and pressures, with enhanced nucleation rates at very large pressures. This implies a slower progression of silicate dust formation in stellar environments than previously assumed.

[170] arXiv:1803.04319v1 [pdf, vox]

Recognizing the Value of the Solar Gravitational Lens for Direct Multipixel Imaging and Spectroscopy of an Exoplanet

Slava G. Turyshev, Michael Shao, Janice Shen, Hanying Zhou, Viktor T. Toth, Louis Friedman, Leon Alkalai, Nitin Arora, Darren D. Garber, Henry Helvajian, Thomas Heinsheimer, Siegfried W. Janson, Les Johnson, Jared R. Males, Roy Nakagawa, Seth Redfield, Nathan Strange, Mark R. Swain, David Van Buren, John L. West, Stacy Weinstein-Weiss
Submitted Monday 12 March 2018 @ 15:42:07 GMT
A White Paper to the National Academy of Sciences Committee on an Exoplanet Science Strategy Call for Papers. 6 pages, 3 figures

The Solar Gravitational Lens (SGL) allows for major brightness amplification ($\sim 10^{11}$ at wavelength of $1~\mu$m) and extreme angular resolution ($\sim10^{-10}$ arcsec) within a narrow field of view. A meter-class telescope, with a modest coronagraph to block solar light with 1e-6 suppression placed in the focal area of the SGL, can image an exoplanet at a distance of 30 parsec with few kilometer-scale resolution on its surface. Notably, spectroscopic broadband SNR is $\sim 10^{-6}$ in two weeks of integration time, providing this instrument with incredible remote sensing capabilities. A mission capable of exploiting the remarkable optical properties of the SGL allows for direct high-resolution imaging/spectroscopy of a potentially habitable exoplanet. Such missions could allow exploration of exoplanets relying on the SGL capabilities decades, if not centuries, earlier than possible with other extant technologies.

[171] arXiv:1803.04301v1 [pdf, vox]

Dynamical evolution of stars and gas of young embedded stellar sub-clusters

Alison Sills, Steven Rieder, Jennifer Scora, Jessica McCloskey, Sarah Jaffa
Submitted Monday 12 March 2018 @ 15:12:42 GMT
Accepted for publication in MNRAS. 11 pages, 13 figures, 2 tables

We present simulations of the dynamical evolution of young embedded star clusters. Our initial conditions are directly derived from X-ray, infrared, and radio observations of local systems, and our models evolve both gas and stars simultaneously. Our regions begin with both clustered and extended distributions of stars, and a gas distribution which can include a filamentary structure in addition to gas surrounding the stellar subclusters. We find that the regions become spherical, monolithic, and smooth quite quickly, and that the dynamical evolution is dominated by the gravitational interactions between the stars. In the absence of stellar feedback, the gas moves gently out of the centre of our regions but does not have a significant impact on the motions of the stars at the earliest stages of cluster formation. Our models at later times are consistent with observations of similar regions in the local neighbourhood. We conclude that the evolution of young proto-star clusters is relatively insensitive to reasonable choices of initial conditions. Models with more realism, such as an initial population of binary and multiple stars and ongoing star formation, are the next step needed to confirm these findings.

[172] arXiv:1803.04296v1 [pdf, vox]

Quantization bias for digital correlators

J. Mena-Parra, K. Bandura, M. A. Dobbs, J. R. Shaw, S. Siegel
Submitted Monday 12 March 2018 @ 14:53:26 GMT
19 pages, 8 figures. Submitted to JAI

In radio interferometry, the quantization process introduces a bias in the magnitude and phase of the measured correlations which translates into errors in the measurement of source brightness and position in the sky, affecting both the system calibration and image reconstruction. In this paper we investigate the biasing effect of quantization in the measured correlation between complex-valued inputs with a circularly symmetric Gaussian probability density function (PDF), which is the typical case for radio astronomy applications. We start by calculating the correlation between the input and quantization error and its effect on the quantized variance, first in the case of a real-valued quantizer with a zero mean Gaussian input and then in the case of a complex-valued quantizer with a circularly symmetric Gaussian input. We demonstrate that this input-error correlation is always negative for a quantizer with an odd number of levels, while for an even number of levels this correlation is positive in the low signal level regime. In both cases there is an optimal interval for the input signal level for which this input-error correlation is very weak and the model of additive uncorrelated quantization noise provides a very accurate approximation. We determine the conditions under which the magnitude and phase of the measured correlation have negligible bias with respect to the unquantized values: we demonstrate that the magnitude bias is negligible only if both unquantized inputs are optimally quantized (i.e., when the uncorrelated quantization error model is valid), while the phase bias is negligible when 1) at least one of the inputs is optimally quantized, or when 2) the correlation coefficient between the unquantized inputs is small. Finally, we determine the implications of these results for radio interferometry.

[173] arXiv:1803.04294v1 [pdf, vox]

Imprints of relativistic effects on the asymmetry of the halo cross-correlation function: from linear to non-linear scales

Michel-Andrès Breton, Yann Rasera, Atsushi Taruya, Osmin Lacombe, Shohei Saga
Submitted Monday 12 March 2018 @ 14:52:15 GMT
29 pages, 23 figures

The apparent distribution of large-scale structures in the universe is sensitive to the velocity/potential of the sources as well as the potential along the line-of-sight through the mapping from real space to redshift space (redshift-space distortions, RSD). Since odd multipoles of the halo cross-correlation function vanish when considering standard Doppler RSD, the dipole is a sensitive probe of relativistic and wide-angle effects. We build a catalog of ten million halos (Milky-Way size to galaxy-cluster size) from the full-sky light-cone of a new "RayGalGroupSims" N-body simulation which covers a volume of ($2.625~h^{-1}$Gpc)$​^3$ with $4096^3$ particles. Using ray-tracing techniques, we find the null geodesics connecting all the sources to the observer. We then self-consistently derive all the relativistic contributions (in the weak-field approximation) to RSD: Doppler, transverse Doppler, gravitational, lensing and integrated Sachs-Wolfe. It allows us, for the first time, to disentangle all contributions to the dipole from linear to non-linear scales. At large scale, we recover the linear predictions dominated by a contribution from the divergence of neighbouring line-of-sights. While the linear theory remains a reasonable approximation of the velocity contribution to the dipole at non-linear scales it fails to reproduce the potential contribution below $30-60~h^{-1}$Mpc (depending on the halo mass). At scales smaller than $\sim 10~h^{-1}$Mpc, the dipole is dominated by the asymmetry caused by the gravitational redshift. The transition between the two regimes is mass dependent as well. We also identify a new non-trivial contribution from the non-linear coupling between potential and velocity terms.

[174] arXiv:1803.04288v1 [pdf, vox]

Structural changes in the hot Algol OGLE-LMC-DPV-097 and its disk related to its long-cycle

J. Garcés L., R. E. Mennickent, G. Djurasević, R. Poleski, I. Soszyński
Submitted Monday 12 March 2018 @ 14:43:22 GMT
Accepted for publication in MNRAS letters. 4 pages, 4 figures, 2 tables

Double Periodic Variables (DPVs) are hot Algols showing a long photometric cycle of uncertain origin. We report the discovery of changes in the orbital light curve of OGLE-LMC-DPV-097 which depend on the phase of its long photometric cycle. During the ascending branch of the long-cycle the brightness at the first quadrature is larger than during the second quadrature, during the maximum of the long-cycle the brightness is basically the same at both quadratures, during the descending branch the brightness at the second quadrature is larger than during the first quadrature and during the minimum of the long-cycle the secondary minimum disappears. We model the light curve at different phases of the long-cycle and find that the data are consistent with changes in the properties of the accretion disk and two disk spots. The disk's size and temperature change with the long-cycle period. We find a smaller and hotter disk at minimum and larger and cooler disk at maximum. The spot temperatures, locations and angular sizes also show variability during the long-cycle.

[175] arXiv:1803.04286v1 [pdf, vox]

Extremely $^{54}$Cr- and $^{50}$Ti-rich presolar oxide grains in a primitive meteorite: Formation in rare types of supernovae and implications for the astrophysical context of solar system birth

Larry R. Nittler, Conel M. O'D. Alexander, Nan Liu, Jianhua Wang
Submitted Monday 12 March 2018 @ 14:42:05 GMT
Accepted for publication in The Astrophysical Journal Letters; 14 pp, including 1 table and 4 figures

We report the identification of 19 presolar oxide grains from the Orgueil CI meteorite with substantial enrichments in $^{54}$Cr, with $^{54}$Cr/$^{52}$Cr ratios ranging from 1.2 to 56 times the solar value. The most enriched grains also exhibit enrichments at mass 50, most likely due in part to $^{50}$Ti, but close-to-normal or depleted $^{53}$Cr/$^{52}$Cr ratios. There is a strong inverse relationship between $^{54}$Cr enrichment and grain size; the most extreme grains are all <80 nm in diameter. Comparison of the isotopic data with predictions of nucleosynthesis calculations indicate that these grains most likely originated in either rare, high-density Type Ia supernovae (SNIa), or in electron-capture supernovae (ECSN) which may occur as the end stage of evolution for stars of mass 8-10 M$_\odot$. This is the first evidence for preserved presolar grains from either type of supernova. An ECSN origin is attractive since these likely occur much more frequently than high-density SNIa, and their evolutionary timescales ($\sim$20 Myr) are comparable to those of molecular clouds. Self-pollution of the Sun's parent cloud from an ECSN may explain the heterogeneous distribution of n-rich isotopic anomalies in planetary materials, including a recently reported dichotomy in Mo isotopes in the solar system. The stellar origins of three grains with solar $^{54}$Cr/$^{52}$Cr, but anomalies in $^{50}$Cr or $^{53}$Cr, as well as of a grain enriched in $^{57}$Fe, are unclear.

[176] arXiv:1803.04278v1 [pdf, vox]

Survival of a planet in short-period Neptunian desert under effect of photo-evaporation

Dmitry E. Ionov, Yaroslav N. Pavlyuchenkov, Valery I. Shematovich
Submitted Monday 12 March 2018 @ 14:22:26 GMT
accepted for publication in MNRAS, 6 pages, 3 figures

Despite the identification of a great number of Jupiter-like and Earth-like planets at close-in orbits, the number of "hot Neptunes" - the planets with 0.6-18 times of Neptune mass and orbital periods less than 3 days - turned out to be very small. The corresponding region in the mass-period distribution was assigned as the "short-period Neptunian desert". The common explanation of this fact is that the gaseous planet with few Neptune masses would not survive in the vicinity of host star due to intensive atmosphere outflow induced by heating from stellar radiation. To check this hypothesis we performed numerical simulations of atmosphere dynamics for a hot Neptune. We adopt the previously developed self-consistent 1D model of hydrogen-helium atmosphere with suprathermal electrons accounted. The mass-loss rates as a function of orbital distances and stellar ages are presented. We conclude that the desert of short-period Neptunes could not be entirely explained by evaporation of planet atmosphere caused by the radiation from a host star. For the less massive Neptune-like planet, the estimated upper limits of the mass loss may be consistent with the photo-evaporation scenario, while the heavier Neptune-like planets could not lose the significant mass through this mechanism. We also found the significant differences between our numerical results and widely used approximate estimates of the mass loss.

[177] arXiv:1803.04264v1 [pdf, vox]

Scanamorphos for the APEX-ArTéMiS far-infrared camera : description and user guide

Hélène Roussel
Submitted Monday 12 March 2018 @ 14:02:23 GMT

Scanamorphos is public software initially developed to post-process scan observations performed with the Herschel photometer arrays. This post-processing mainly consists in subtracting the total low-frequency noise (both its thermal and non-thermal components), masking cosmic ray hits, and projecting the data onto a map. Building upon the results obtained for P-ArT\'eMiS (the prototype of ArT\'eMiS), Herschel and then NIKA2 (a resident camera of the IRAM 30-m telescope operating at 1.25 and 2 mm), it has now been tailored to the ArT\'eMiS camera, an ESO and OSO P.I. instrument installed at the APEX 12-m telescope, demonstrating our initial claim that the software principles were directly transposable to scan observations made with other instruments, including from the ground, provided they entail sufficient redundancy. This document explains how the algorithm was modified to cope with the specificities of ArT\'eMiS observations and with the atmospheric emission at 350 and 450 $\mu$m, far dominating the instrumental drifts that were the only low-frequency noise component in Herschel data. Like in the original software, this was accomplished without assuming any noise model and without applying any Fourier-space filtering, by exploiting the redundancy built in the observations - taking advantage of the fact that each portion of the sky is sampled at multiple times by multiple bolometers. It remains an interactive software in the sense that the user is allowed to optionally visualize and control results at each intermediate step, but the processing is fully automated. It has been grafted onto the ArT\'eMiS pipeline, in charge of the formatting, calibration and projection of the data, that is described elsewhere.

[178] arXiv:1803.04229v1 [pdf, vox]

Asymptotic theory of gravity modes in rotating stars II. Impact of general differential rotation

Vincent Prat, Stéphane Mathis, Kyle Augustson, François Lignières, Jérôme Ballot, Lucie Alvan, Allan Sacha Brun
Submitted Monday 12 March 2018 @ 12:50:18 GMT
17 pages, 12 figures, accepted for publication in A&A

Context. Differential rotation has a strong influence on stellar internal dynamics and evolution, notably by triggering hydrodynamical instabilities, by interacting with the magnetic field, and more generally by inducing transport of angular momentum and chemical elements. Moreover, it modifies the way waves propagate in stellar interiors and thus the frequency spectrum of these waves, the regions they probe, and the transport they generate. Aims. We investigate the impact of a general differential rotation (both in radius and latitude) on the propagation of axisymmetric gravito-inertial waves. Methods. We use a small-wavelength approximation to obtain a local dispersion relation for these waves. Then, we describe the propagation of waves thanks to a ray model that follows a Hamiltonian formalism. Finally, we numerically probe the properties of these gravito-inertial rays for different regimes of radial and latitudinal differential rotation. Results. We derive a local dispersion relation that includes the effect of a general differential rotation. Then, considering a polytropic stellar model, we observe that differential rotation allows for a large variety of resonant cavities that can be probed by gravito-inertial waves. We identify that for some regimes of frequency and differential rotation, the properties of gravito-inertial rays are similar to the ones found in the uniformly rotating case. Yet we also find new regimes specific to differential rotation, where the dynamics of rays is chaotic. Conclusions. As a consequence, we expect modes to follow the same trend. Some parts of oscillation spectra corresponding to regimes similar to those of the uniformly rotating case would exhibit regular patterns, while parts corresponding to the new regimes would be mostly constituted of chaotic modes with a spectrum rather characterised by a generic statistical distribution.

[179] arXiv:1803.04197v1 [pdf, vox]

Degeneracies between Modified Gravity and Baryonic Physics

Thor A. S. Ellewsen, Bridget Falck, David F. Mota
Submitted Monday 12 March 2018 @ 11:21:47 GMT
9 pages, 4 figures, accepted to A&A

In order to determine the observable signatures of modified gravity theories, it is important to consider the effect of baryonic physics. We use a modified version of the ISIS code to run cosmological hydrodynamic simulations to study degeneracies between modified gravity and radiative hydrodynamical processes. Of these, one was the standard $\Lambda$CDM model and four were variations of the Symmetron model. For each model we ran three variations of baryonic processes: non-radiative hydrodynamics; cooling and star formation; and cooling, star formation, and supernova feedback. We construct stacked gas density, temperature, and dark matter density profiles of the halos in the simulations, and study the differences between them. We find that both radiative variations of the models show degeneracies between their processes and at least two of the three parameters defining the Symmetron model.

[180] arXiv:1803.04177v1 [pdf, vox]

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).III. Star formation in the stripped gas of NGC 4254

A. Boselli, M. Fossati, J. C. Cuillandre, S. Boissier, M. Boquien, V. Buat, D. Burgarella, G. Consolandi, L. Cortese, P. Cote, S. Cote, P. Durrell, L. Ferrarese, M. Fumagalli, G. Gavazzi, S. Gwyn, G. Hensler, B. Koribalski, J. Roediger, Y. Roehlly, D. Russeil, M. Sun, E. Toloba, B. Vollmer, A. Zavagno
Submitted Monday 12 March 2018 @ 10:47:05 GMT
Accepted for publication on Astronomy & Astrophysics

During pilot observations of the Virgo Environmental Survey Tracing Galaxy Evolution (VESTIGE), a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we have observed the spiral galaxy NGC 4254 (M99). Deep Halpha+[NII] narrow-band and GALEX UV images revealed the presence of 60 compact (70-500 pc radius) star forming regions up to ~ 20 kpc outside the optical disc of the galaxy. These regions are located along a tail of HI gas stripped from the disc of the galaxy after a rapid gravitational encounter with another Virgo cluster member that simulations indicate occurred 280-750 Myr ago. We have combined the VESTIGE data with multifrequency data from the UV to the far-infrared to characterise the stellar populations of these regions and study the star formation process in an extreme environment such as the tails of stripped gas embedded in the hot intracluster medium. The colour, spectral energy distribution (SED), and linear size consistently indicate that these regions are coeval and have been formed after a single burst of star formation that occurred ~< 100 Myr ago. These regions might become free floating objects within the cluster potential well, and be the local analogues of compact sources produced after the interaction of gas-rich systems that occurred during the early formation of clusters.

[181] arXiv:1803.05306v1 [pdf, vox]

On the Development of Testing Tool for a Satellite Gyro Sensor

Harry Septanto, Desti Ika Suryanti
Submitted Monday 12 March 2018 @ 09:13:49 GMT

Attitude determination and control system (ADCS) in a satellite takes an important role to make sure that the satellite mission will be achieved. In the development phase, the ADCS is required to pass whole testing levels, including component level verification. As an important component in the ADCS, the gyro sensors must meet in that requirement. However, the testing tool for the component level test often rely on another satellite component. Since the testing line is not directly connected to the gyro, some failures between those components will be hard to be identified. This paper proposes a testing tool that operates without involves any other satellite components. The proposed testing tool consists of software and hardware part.

[182] arXiv:1803.02981v2 [pdf, vox]

The Role of Galaxies and AGN in Reionising the IGM - I: Keck Spectroscopy of 5 < z < 7 Galaxies in the QSO Field J1148+5251

Koki Kakiichi, Richard S. Ellis, Nicolas Laporte, Adi Zitrin, Anna-Christina Eilers, Emma Ryan-Weber, Romain A. Meyer, Brant Robertson, Daniel P. Stark, Sarah E. I. Bosman
Submitted Monday 12 March 2018 @ 08:44:33 GMT
21 pages, 16 figures, submitted to MNRAS (figure size reduced)

We introduce a new method for determining the influence of galaxies and active galactic nuclei (AGN) on the physical state of the intergalactic medium (IGM) at high redshift and illustrate its potential via a first application to the field of the $z=6.42$ QSO J1148+5251. By correlating the spatial positions of spectroscopically-co​nfirmed Lyman break galaxies (LBGs) with fluctuations in the Lyman alpha forest seen in the high signal-to-noise spectrum of a background QSO, we provide a statistical measure of the typical escape fraction of Lyman continuum photons close to the end of cosmic reionisation. Here we use Keck DEIMOS spectroscopy to locate 7 colour-selected LBGs in the redshift range $5.3\lesssim z\lesssim 6.4$ and confirm a faint $z=5.701$ AGN. We then examine the spatial correlation between this sample and Ly$\alpha$/Ly$\beta$ transmission fluctuations in a Keck ESI spectrum of the QSO. Interpreting the statistical HI proximity effect as arising from faint galaxies clustered around the detected LBGs, we translate the observed mean Ly$\alpha$ transmitted flux around an average detected LBG into a constraint on the mean escape fraction $\langle f_{\rm esc}\rangle\geq0.08$ at $z\simeq6$. We also report evidence of the individual transverse HI proximity effect of a $z=6.177$ luminous LBG via a Ly$\beta$ transmission spike and two broad Ly$\alpha$ transmission spikes around the $z=5.701$ AGN. We discuss the possible origin of such associations which suggest that while faint galaxies are primarily driving reionisation, luminous galaxies and AGN may provide important contributions to the UV background or thermal fluctuations of the IGM at $z\simeq6$. Although a limited sample, our results demonstrate the potential of making progress using this method in resolving one of the most challenging aspects of the contribution of galaxies and AGN to cosmic reionisation.

[183] arXiv:1803.04134v1 [pdf, vox]

Diagnostics for generalized power-law torsion-matter coupling $f(T)$ model

Xiang-Hua Zhai, Qiang Wen, Rui-Hui Lin, Xin-Zhou Li
Submitted Monday 12 March 2018 @ 07:11:08 GMT
9 pages,12 figures

The currently accelerated expansion of our Universe is unarguably one of the most intriguing problems in today's physics research. Two realistic non-minimal torsion-matter coupling $f(T)$ models have been established and studied in our previous papers [Phys. Rev. D92, 104038(2015) and Eur. Phys. J. C77, 504(2017)] aiming to explain this "dark energy" problem. In this paper, we study the generalized power-law torsion-matter coupling $f(T)$ model. Dynamical system analysis shows that the three expansion phases of the Universe, i.e. the radiation dominated era, the matter dominated era and the dark energy dominated era, can all be reproduced in this generalized model. By using the statefinder and $Om$ diagnostics, we find that the different cases of the model can be distinguished from each other and from other dark energy models such as the two models in our previous papers, $\Lambda$CDM, quintessence and Chaplygin gas. Furthermore, the analyses also show that all kinds of generalized power-law torsion-matter coupling model are able to cross the $w=-1$ divide from below to above, thus the decrease of the energy density resulting from the crossing of $w$ will make the catastrophic fate of the Universe avoided and a de Sitter expansion fate in the future will be approached.

[184] arXiv:1803.04127v1 [pdf, vox]

Magnesium isotopes: a tool to understand self-enrichment in Globular Clusters

Paolo Ventura, Franca D'Antona, Gianluca Imbriani, Marcella Di Criscienzo, Flavia Dell'Agli, Marco Tailo
Submitted Monday 12 March 2018 @ 06:21:37 GMT
accepted for publication on MNRAS

A critical issue in the asymptotic giant branch (AGB) self-enrichment scenario for the formation of multiple populations in Globular Clusters (GCs) is the inability to reproduce the magnesium isotopic ratios, despite the model in principle can account for the depletion of magnesium. In this work we analyze how the uncertainties on the various p-capture cross sections affect the results related to the magnesium content of the ejecta of AGB stars. The observed distribution of the magnesium isotopes and of the overall Mg-Al trend in M13 and NGC 6752 are successfully reproduced when the proton-capture rate by 25Mg at the temperatures 100 MK, in particular the 25Mg(p, gamma)26Alm channel, is enhanced by a factor 3 with respect to the most recent experimental determinations. This assumption also allows to reproduce the full extent of the Mg spread and the Mg-Si anticorrelation observed in NGC 2419. The uncertainties in the rate of the 25Mg(p,gamma)26Alm reaction at the temperatures of interest here leave space for our assumption and we suggest that new experimental measurements are needed to settle this problem. We also discuss the competitive model based on the super massive star nucleosynthesis.

[185] arXiv:1803.04112v1 [pdf, vox]

Hadronic origin of prompt high-energy emission of gamma-ray bursts revisited: in the case of a limited maximum proton energy

Kai Wang, Ruo-Yu Liu, Zi-Gao Dai, Katsuaki Asano
Submitted Monday 12 March 2018 @ 04:51:25 GMT
36 pages, 13 figures, accepted for publication in ApJ

The high-energy (> 100MeV) emission observed by Fermi-LAT during the prompt phase of some luminous gamma-ray bursts (GRBs) could arise from the cascade induced by interactions between accelerated protons and the radiation field of GRBs. The photomeson process, which is usually suggested to operate in such a hadronic explanation, requires a rather high proton energy (> 10^17eV) for an efficient interaction. However, whether GRBs can accelerate protons to such a high energy is far from guaranteed, although they have been suggested as the candidate source for ultrahigh-energy cosmic rays. In this work, we revisit the hadronic model for the prompt high-energy emission of GRBs with a smaller maximum proton energy than the usually adopted value estimated from the Bohm condition. In this case, the Bethe-Heitler pair production process becomes comparably important or even dominates over the photomeson process. We show that with a relatively low maximum proton energy with a Lorentz factor of 10^5 in the comoving frame, the cascade emission can still reproduce various types of high-energy spectrum of GRBs. For most GRBs without high-energy emission detected, the maximum proton energy could be even lower and relax the constraints on the parameters of GRB jet resulting from the fact of non-detection of GRB neutrinos by IceCube.

[186] arXiv:1803.04109v1 [pdf, vox]

What is parameterized $Om(z)$ diagnostics telling us in light of recent observations?

Jing-Zhao Qi, Shuo Cao, Marek Biesiada, Tengpeng Xu, Yan Wu, Sixuan Zhang, Zong-Hong Zhu
Submitted Monday 12 March 2018 @ 03:57:45 GMT
14 pages, 6 figures, to be published in RAA

In this paper, we propose a new parametrization of $Om(z)$ diagnostics and show how the most recent and significantly improved observations concerning the $H(z)$ and SN Ia measurements can be used to probe the consistency or tension between $\Lambda$CDM model and observations. Our results demonstrates that $H_0$ plays a very important role in the consistency test of $\Lambda$CDM with the $H(z)$ data. Adopting the Hubble constant priors from \textit{Planck} 2013 and Riess (2016), one finds a considerable tension between the current $H(z)$ data and $\Lambda$CDM model and confirms the conclusions obtained previously by the others. However, with the Hubble constant prior taken from WMAP9, the discrepancy between $H(z)$ data and $\Lambda$CDM disappears, i.e., the current $H(z)$ observations still support the cosmological constant scenario. This conclusion is also supported by the results derived from the JLA SNe Ia sample. The best-fit Hubble constant from the combination of $H(z)$+JLA ($H_0=68.81^{+1.50}_​{-1.49}$ km/s/Mpc) is well consistent with the results derived both by Planck 2013 and WMAP9, which is significantly different from the recent local measurement by Riess (2016).

[187] arXiv:1803.04091v1 [pdf, vox]

Planetary Candidates from K2 Campaign 16

Liang Yu, Ian J. M. Crossfield, Joshua E. Schlieder, Molly R. Kosiarek, Adina D. Feinstein, John H. Livingston, Andrew W. Howard, Björn Benneke, Erik A. Petigura, Charles A. Beichman, David A. Berardo, Makennah Bristow, Jessie L. Christiansen, David R. Ciardi, Justin R. Crepp, Courtney D. Dressing, Benjamin J. Fulton, Erica J. Gonzales, Kevin K. Hardegree-Ullman, Thomas Henning, Howard Isaacson, Heather A. Knutson, Sébastien Lépine, Arturo O. Martinez, Farisa Y. Morales, Rahul I. Patel, Evan Sinukoff, Michael W. Werner
Submitted Monday 12 March 2018 @ 02:25:10 GMT
17 pages, 7 figures, 5 tables, submitted to AJ

We present a catalog of interesting targets recently identified using data from Campaign 16 of the K2 mission. Our catalog includes 32 high-quality planet candidates (showing no signs of being non- planetary in nature), 54 more ambiguous events that may be either planets or false positives, 169 eclipsing binaries, and 217 other regularly periodic variable sources. We have released light curves for all targets in C16, and have also released system parameters and transit vetting plots for all interesting candidates identified in this paper. Of particular interest is a candidate planet orbiting the bright F dwarf HD 73344 (V = 6.9, K = 5.6) with an orbital period of 15 days. If confirmed, this object would correspond to a $\sim2.6 R_{\oplus}$ planet and would likely be a favorable target for radial velocity characterization. Campaign 16 is one of just two K2 campaigns observed so far in "forward-facing" mode, which enables immediate follow-up observations from the ground. This paper is intended as a rapid release of planet candidates, eclipsing binaries and other interesting periodic variables to maximize the scientific yield of this campaign, and as a test run for the upcoming TESS mission, whose frequent data releases call for similarly rapid candidate identification and efficient follow-up.

[188] arXiv:1803.04088v1 [pdf, vox]

Pre-Eruptive Magnetic Reconnection within a Multi-Flux-Rope System in the Solar Corona

Arun Kumar Awasthi, Rui Liu, Haimin Wang, Yuming Wang, Chenglong Shen
Submitted Monday 12 March 2018 @ 01:58:51 GMT
Accepted for publication in ApJ

The solar corona is frequently disrupted by coronal mass ejections (CMEs), whose core structure is believed to be a flux rope made of helical magnetic field. This has become a "standard" picture although it remains elusive how the flux rope forms and evolves toward eruption. While 1/3 of the ejecta passing through spacecrafts demonstrate a flux-rope structure, the rest have complex magnetic fields. Are they originating from a coherent flux rope, too? Here we investigate the source region of a complex ejecta, focusing on a flare precursor with definitive signatures of magnetic reconnection, i.e., nonthermal electrons, flaring plasma, and bi-directional outflowing blobs. Aided by nonlinear force-free field modeling, we conclude that the reconnection occurs within a system of multiple braided flux ropes with different degree of coherency. The observation signifies the importance of internal structure and dynamics in understanding CMEs and in predicting their impacts on Earth.

Submitted Sun, 11 Mar 2018

[189] arXiv:1803.04055v1 [pdf, vox]

Kinematics of B-F Stars as a Function of Their Dereddened Color from Gaia and PCRV Data

George Gontcharov
Submitted Sunday 11 March 2018 @ 22:08:06 GMT
8 figures, published in Astronomy Letters, 2018, 44, 248-264

Parallaxes with an accuracy better than 10% and proper motions from the Gaia DR1 TGAS catalogue, radial velocities from the PCRV, Tycho-2 photometry, PARSEC, MIST, YaPSI, BaSTI isochrones, and the most accurate reddening and extinction estimates have been used to analyze the kinematics of 9543 thin-disk B-F stars as a function of their dereddened color. These stars are located on the Hertzsprung-Russell diagram relative to the isochrones with a high accuracy. This has allowed me to conclude that the reddening and extinction were significantly underestimated in some kinematic studies of other authors. The median accuracy of the velocity components U, V, W in this study is 1.7 km/s, although outside the range $-0.1<(B_T-V_T)_0<0.​5$ the kinematic characteristics are noticeably biased due to the incompleteness of the sample. We have confirmed the variations in the mean velocity of stars relative to the Sun and the stellar velocity dispersion as a function of their dereddened color known from the Hipparcos data. Given the age estimates for the stars under consideration from the TRILEGAL model and the Geneva-Copenhagen survey, these variations may be considered as variations as a function of the age. A comparison of our results with the results of other studies of the stellar kinematics near the Sun has shown that selection and reddening underestimation explain almost completely the discrepancies between the results. The dispersions and mean velocities from the results of reliable studies fit into a $\pm2$ km/s corridor, while the ratios $\sigma_V/\sigma_U$ and $\sigma_W/\sigma_U$ fit into $\pm0.05$. Based on all reliable studies in the range $-0.1<(B_T-V_T)_0<0.​5$, i.e., for an age from 0.23 to 2.4 Gyr, we have found that the stellar velocity dispersions in km/s are proportional to the age in Gyr raised to the power $\beta_U=0.33$, $\beta_V=0.285$, and $\beta_W=0.37$.

[190] arXiv:1803.04010v1 [pdf, vox]

Towards completing Planetary Systems: The role of minor bodies on life growth and survival

Jorge Lillo-Box, David Kipping, Isabel Rebollido, Pedro Figueira, Adrien Leleu, Alexandre Correia, Philippe Robutel, Nuno C. Santos, David Barrado, Benjamín Montesinos, Tjarda Boekholt
Submitted Sunday 11 March 2018 @ 18:49:49 GMT
5 pages; White paper submitted in response to the solicitation of feedback for the "Exoplanet Science Strategy" by the National Academy of Sciences, Engineering, and Medicine; March, 2018. http://sites.nationa​​urrentProjects/SSB_1​80659

The search for extrasolar planets in the past decades has shown that planets abound in the Solar neighborhood. While we are still missing an Earth twin, the forthcoming space missions and ground-based instrumentation are already driven to achieve this goal. But, in order to fully understand the conditions for life appearing in the Solar System, we still miss some pieces of the planetary system jigsaw puzzle, namely a deeper understanding of the minor bodies. Trojans, moons, and comets are tracers of the formation and evolution processes of planetary systems. These missing pieces are also critical to understand the emergence and evolution of life over millions of years. With the large crop of planetary systems discovered so far and yet to be detected with the forthcoming missions, the hunt for minor bodies in extrasolar systems is a natural continuation of our search for real Solar System- and, in particular, Earth- analogs. This white paper is focused on detection of these minor components and their relevance in the emergence, evolution and survival of life.

[191] arXiv:1803.04003v1 [pdf, vox]

Precise Near-Infrared Radial Velocities with iSHELL

Bryson Cale, Peter Plavchan, Jonathan Gagné, Eric Gaidos, Angelle Tanner, Peter Gao
Submitted Sunday 11 March 2018 @ 18:25:47 GMT
White Paper submitted to the SSB

We present a possible NASA key project using the iSHELL near-infrared high-resolution echelle spectrograph on the NASA Infrared Telescope Facility for precise radial velocity follow-up of candidate transiting exoplanets identified by the NASA TESS mission. We briefly review key motivations and challenges with near-infrared radial velocities. We present the current status of our preliminary radial velocity analysis from the first year on sky with iSHELL.

[192] arXiv:1803.03967v1 [pdf, vox]

A multi-wavelength study of the evolution of Early-Type Galaxies in Groups: the ultraviolet view

R. Rampazzo, P. Mazzei, A. Marino, L. Bianchi, H. Plana, G. Trinchieri, M. Uslenghi, A. Wolter
Submitted Sunday 11 March 2018 @ 14:30:07 GMT
12 pages, 6 figures: accepted for publication in Astrophysics & Space Science as contributions to the workshop: "UV astronomy, the needs and the means"

ABRIDGED- The UV-optical color magnitude diagram (CMD) of rich galaxy groups is characterised by a well developed Red Sequence (RS), a Blue Cloud (BC) and the so-called Green Valley (GV). Loose, less evolved groups of galaxies likely not virialized yet may lack a well defined RS. This is actually explained in the framework of galaxy evolution. We are focussing on understanding galaxy migration towards the RS, checking for signatures of such a transition in their photometric and morphological properties. We report on the UV properties of a sample of ETGs galaxies inhabiting the RS. The analysis of their structures, as derived by fitting a Sersic law to their UV luminosity profiles, suggests the presence of an underlying disk. This is the hallmark of dissipation processes that still must have a role in the evolution of this class of galaxies. SPH simulations with chemo-photometric implementations able to match the global properties of our targets are used to derive their evolutionary paths through UV-optical CDM, providing some fundamental information such as the crossing time through the GV, which depends on their luminosity. The transition from the BC to the RS takes several Gyrs, being about 3-5 Gyr for the the brightest galaxies and more long for fainter ones, if it occurs. The photometric study of nearby galaxy structures in UV is seriously hampered by either the limited FoV of the cameras (e.g in HST) or by the low spatial resolution of the images (e.g in the GALEX). Current missions equipped with telescopes and cameras sensitive to UV wavelengths, such as Swift-UVOT and Astrosat-UVIT, provide a relatively large FoV and better resolution than the GALEX. More powerful UV instruments (size, resolution and FoV) are obviously bound to yield fundamental advances in the accuracy and depth of the surface photometry and in the characterisation of the galaxy environment.

[193] arXiv:1803.03964v1 [pdf, vox]

Multiband optical flux and polarization variability of the blazar OJ 287 during 2016 - 2017

Alok C. Gupta, Haritma Gaur, Paul J. Wiita, A. Pandey, P. Kushwaha, S. M. Hu, O. M. Kurtanidze, E. Semkov, G. Damljanovic, A. Goyal, M. Uemura, A. Darriba, Xu Chen, O. Vince, M. F. Gu, Z. Zhang, R. Bachev, R. Itoh, M. Kawabata, S. O. Kurtanidze, T. Nakaoka, M. G. Nikolashvili, L. A. Sigua, L. Stawarz, A. Strigachev
Submitted Sunday 11 March 2018 @ 14:14:24 GMT
14 pages, 8 figures, 7 tables; Submitted to MNRAS

We report on our recent multi-band optical photometric and polarimetric observational campaign of the blazar OJ 287 which was carried out during September 2016 -- December 2017. We employed nine telescopes in Bulgaria, China, Georgia, Japan, Serbia, Spain and the United States. We collected over 1800 photometric image frames in BVRI bands and over 100 polarimetric measurements over ~ 175 nights. In 11 nights with many quasi-simultaneous multi-band (V, R, I) observations, we did not detect any genuine intraday variability in flux or colour. On longer timescales multiple flaring events were seen. Large changes in colour with respect to time and in a colour--magnitude diagram were seen, and while no systematic variability trend was noticed in colour with respect to time, the colour--magnitude diagram shows a bluer-when-brighter trend. Large changes in the degree of polarization, and substantial swings in the polarization angle were detected. The fractional Stokes parameters of the polarization showed a systematic trend with time in the beginning of these observations, followed by chaotic changes and then an apparently systematic variation at the end. The spectral index shows a systematic variation with time and V-band magnitude and optical spectral energy distributions in outburst states, an intermediate state, and a low flux state, all show evidence of a blue bump. We briefly discuss possible physical mechanisms that could explain the observed flux, colour, polarization, and spectral variability.

[194] arXiv:1803.03960v1 [pdf, vox]

EarthFinder: A Precise Radial Velocity Probe Mission Concept For the Detection of Earth-Mass Planets Orbiting Sun-like Stars

Peter Plavchan, Bryson Cale, Patrick Newman, Bahaa Hamze, Natasha Latouf, William Matzko, Chas Beichman, David Ciardi, Bill Purcell, Paul Lightsey, Heather Cegla, Xavier Dumusque, Vincent Bourrier, Courtney Dressing, Peter Gao, Gautam Vasisht, Stephanie Leifer, Sharon Wang, Jonathan Gagne, Samantha Thompson, Jonathan Crass, Andrew Bechter, Eric Bechter, Cullen Blake, Sam Halverson, Andrew Mayo, Thomas Beatty, Jason T Wright, Alex Wise, Angelle Tanner, Jason Eastman, Sam Quinn, Debra Fischer, Sarbani Basu, Sophia Sanchez-Maes, Andrew Howard, Kerry Vahala, Ji Wang, Scott Diddams, Scott Papp, Benjamin JS Pope, Emily Martin, Simon Murphy
Submitted Sunday 11 March 2018 @ 13:36:39 GMT
Submitted to the National Academies Committee on Exoplanet Science Strategy

EarthFinder is a Probe Mission concept selected for study by NASA for input to the 2020 astronomy decadal survey. This study is currently active and a final white paper report is due to NASA at the end of calendar 2018. We are tasked with evaluating the scientific rationale for obtaining precise radial velocity (PRV) measurements in space, which is a two-part inquiry: What can be gained from going to space? What can't be done form the ground? These two questions flow down to these specific tasks for our study - Identify the velocity limit, if any, introduced from micro- and macro-telluric absorption in the Earth's atmosphere; Evaluate the unique advantages that a space-based platform provides to emable the identification and mitigation of stellar acitivity for multi-planet signal recovery.

[195] arXiv:1803.03946v1 [pdf, vox]

Explaining the morphology of supernova remnant (SNR) 1987A with the jittering jets explosion mechanism

Ealeal Bear, Noam Soker
Submitted Sunday 11 March 2018 @ 11:45:08 GMT
To be submitted in 2 days to allow comments from readers

We find that the remnant of supernova (SN) 1987A share some morphological features with four supernova remnants (SNRs) that have signatures of shaping by jets, and from that we strengthen the claim that jets played a crucial role in the explosion of SN 1987A. Some of the morphological features appear also in planetary nebulae where jets are observed. The clumpy ejecta bring us to support the claim that the jittering jets explosion mechanism can account for the structure of the remnant of SN 1987A, i.e., SNR 1987A. We conduct a preliminary attempt to quantify the fluctuations in the angular momentum of the mass that is accreted on to the newly born neutron star via an accretion disk or belt. The accretion disk/belt launches the jets that explode core collapse supernovae (CCSNe). The relaxation time of the accretion disk/belt is comparable to the duration of a typical jet-launching episode in the jittering jets explosion mechanism, and hence the disk/belt has no time to relax. We suggest that this might explain unequal two opposite jets that later lead to unequal sides of the elongated structures in SNR of CCSNe. We reiterate our earlier call for a paradigm shift from neutrino-driven explosion to a jet-driven explosion of CCSNe.

[196] arXiv:1803.03909v1 [pdf, vox]

Vortex coronagraphs for the Habitable Exoplanet Imaging Mission (HabEx) concept: theoretical performance and telescope requirements

Garreth Ruane, Dimitri Mawet, Bertrand Mennesson, Jeffrey Jewell, Stuart Shaklan
Submitted Sunday 11 March 2018 @ 05:30:02 GMT
accepted for publication in the Journal of Astronomical Telescopes, Instruments, and Systems. arXiv admin note: text overlap with arXiv:1708.05787

The Habitable Exoplanet Imaging Mission (HabEx) concept requires an optical coronagraph that provides deep starlight suppression over a broad spectral bandwidth, high throughput for point sources at small angular separation, and insensitivity to temporally-varying, low-order aberrations. Vortex coronagraphs are a promising solution that perform optimally on off-axis, monolithic telescopes and may also be designed for segmented telescopes with minor losses in performance. We describe the key advantages of vortex coronagraphs on off-axis telescopes: 1) Unwanted diffraction due to aberrations is passively rejected in several low-order Zernike modes relaxing the wavefront stability requirements for imaging Earth-like planets from <10 to >100 pm rms. 2) Stars with angular diameters >0.1 $\lambda/D$ may be sufficiently suppressed. 3) The absolute planet throughput is >10%, even for unfavorable telescope architectures. 4) Broadband solutions ($\Delta\lambda/\lam​bda>0.1$) are readily available for both monolithic and segmented apertures. The latter make use of grayscale apodizers in an upstream pupil plane to provide suppression of diffracted light from amplitude discontinuities in the telescope pupil without inducing additional stroke on the deformable mirrors. We set wavefront stability requirements on the telescope, based on a stellar irradiance threshold set at an angular separation of 3$\pm$0.5 $\lambda/D$ from the star, and discuss how some requirements may be relaxed by trading robustness to aberrations for planet throughput.

Submitted Sat, 10 Mar 2018

[197] arXiv:1803.03860v1 [pdf, vox]

Jets Launching Radius in Low-Power Radio-Loud AGNs in Advection-Dominated Accretion Flows

Truong Le, William Newman, Brinkley Edge
Submitted Saturday 10 March 2018 @ 20:48:58 GMT
16 pages, 9 figures, 3 tables, accepted by MNRAS (Mar. 09, 2018)

Using our theory for the production of relativistic outflows, we estimate the jet launching radius and the inferred mass accretion rate for 52 low-power radio-loud AGNs based on the observed jet powers. Our analysis indicates that (1) a significant fraction of the accreted energy is required to convert the accreted mass to relativistic energy particles for the production of the jets near the event horizon, (2) the jets launching radius moves radially toward the horizon as the mass accretion rate or jets power increases, and (3) no jet/outflow formation is possible beyond 44 gravitational radii.

[198] arXiv:1803.03858v1 [pdf, vox]

Testing One Hypothesis Multiple Times: The Multidimensional Case

Sara Algeri, David A. van Dyk
Submitted Saturday 10 March 2018 @ 19:49:26 GMT

The identification of new rare signals in data, the detection of a sudden change in a trend, and the selection of competing models, are among the most challenging problems in statistical practice. These challenges can be tackled using a test of hypothesis where a nuisance parameter is present only under the alternative, and a computationally efficient solution can be obtained by the "Testing One Hypothesis Multiple times" (TOHM) method. In the one-dimensional setting, a fine discretization of the space of the non-identifiable parameter is specified, and a global p-value is obtained by approximating the distribution of the supremum of the resulting stochastic process. In this paper, we propose a computationally efficient inferential tool to perform TOHM in the multidimensional setting. Here, the approximations of interest typically involve the expected Euler Characteristics (EC) of the excursion set of the underlying random field. We introduce a simple algorithm to compute the EC in multiple dimensions and for arbitrary large significance levels. This leads to an highly generalizable computational tool to perform inference under non-standard regularity conditions.

[199] arXiv:1803.03848v1 [pdf, vox]

WDEC - A code for modeling white dwarf structure and pulsations

Agnes Bischoff-Kim, Michael H. Montgomery
Submitted Saturday 10 March 2018 @ 18:12:01 GMT
10 pages, 9 figures. To appear in the Astronomical Journal

The White Dwarf Evolution Code (WDEC), written in Fortran, makes models of white dwarf stars. It is fast, versatile, and includes the latest physics. The code evolves hot (~ 100,000 K) input models down to a chosen effective temperature by relaxing the models to be solutions of the equations of stellar structure. The code can also be used to obtain g-mode oscillation modes for the models. WDEC has a long history going back to the late 1960's. Over the years, it has been updated and re-packaged for modern computer architectures, and has specifically been used in computationally intensive asteroseismic fitting. Generations of white dwarf astronomers and dozens of publications have made use of the WDEC, although the last true instrument paper is the original one, published in 1975. This paper discusses the history of the code, necessary to understand why it works the way it does, details the physics and features in the code today, and points the reader to where to find the code and a user guide.

[200] arXiv:1803.03842v1 [pdf, vox]

Turbulence in the TW Hya Disk

Kevin M. Flaherty, A. Meredith Hughes, Richard Teague, Jacob B. Simon, Sean M. Andrews, David J. Wilner
Submitted Saturday 10 March 2018 @ 17:35:09 GMT
14 pages, 4 figures, accepted to ApJ

Turbulence is a fundamental parameter in models of grain growth during the early stages of planet formation. As such, observational constraints on its magnitude are crucial. Here we self-consistently analyze ALMA CO(2-1), SMA CO(3-2), and SMA CO(6-5) observations of the disk around TW Hya and find an upper limit on the turbulent broadening of $<$0.08c$_s$ ($\alpha<$0.007 for $\alpha$ defined only within 2-3 pressure scale heights above the midplane), lower than the tentative detection previously found from an analysis of the CO(2-1) data. We examine in detail the challenges of image plane fitting vs directly fitting the visibilities, while also considering the role of the vertical temperature gradient, systematic uncertainty in the amplitude calibration, and assumptions about the CO abundance, as potential sources of the discrepancy in the turbulence measurements. These tests result in variations of the turbulence limit between $<$0.04c$_s$ and $<$0.13c$_s$, consistently lower than the 0.2-0.4c$_s$ found previously. Having ruled out numerous factors, we restrict the source of the discrepancy to our assumed coupling between temperature and density through hydrostatic equilibrium in the presence of a vertical temperature gradient and/or the confinement of CO to a thin molecular layer above the midplane, although further work is needed to quantify the influence of these prescriptions. Assumptions about hydrostatic equilibrium and the CO distribution are physically motivated, and may have a small influence on measuring the kinematics of the gas, but they become important when constraining small effects such as the strength of the turbulence within a protoplanetary disk.

[201] arXiv:1803.03818v1 [pdf, vox]

Nuclear Reactions in the Crusts of Accreting Neutron Stars

R. Lau, M. Beard, S. S. Gupta, H. Schatz, A. V. Afanasjev, E. F. Brown, A. Deibel, L. R. Gasques, G. W. Hitt, W. R. Hix, L. Keek, P. Möller, P. S. Shternin, A. Steiner, M. Wiescher, Y. Xu
Submitted Saturday 10 March 2018 @ 14:54:09 GMT
25 Pages, submitted to Ap. J

X-ray observations of transiently accreting neutron stars during quiescence provide information about the structure of neutron star crusts and the properties of dense matter. Interpretation of the observational data requires an understanding of the nuclear reactions that heat and cool the crust during accretion, and define its nonequilibrium composition. We identify here in detail the typical nuclear reaction sequences down to a depth in the inner crust where the mass density is 2E12 g/cm^3 using a full nuclear reaction network for a range of initial compositions. The reaction sequences differ substantially from previous work. We find a robust reduction of crust impurity at the transition to the inner crust regardless of initial composition, though shell effects can delay the formation of a pure crust somewhat to densities beyond 2E12 g/cm^3. This naturally explains the small inner crust impurity inferred from observations of a broad range of systems. The exception are initial compositions with A >= 102 nuclei, where the inner crust remains impure with an impurity parameter of Qimp~20 due to the N = 82 shell closure. In agreement with previous work we find that nuclear heating is relatively robust and independent of initial composition, while cooling via nuclear Urca cycles in the outer crust depends strongly on initial composition. This work forms a basis for future studies of the sensitivity of crust models to nuclear physics and provides profiles of composition for realistic crust models.

[202] arXiv:1803.03817v1 [pdf, vox]

Fayet-Iliopoulos terms in supergravity and D-term inflation

Ignatios Antoniadis, Auttakit Chatrabhuti, Hiroshi Isono, Rob Knoops
Submitted Saturday 10 March 2018 @ 14:29:24 GMT
19 pages, 7 figures

We analyse the consequences of a new gauge invariant Fayet-Iliopoulos (FI) term proposed recently to a class of inflation models driven by supersymmetry breaking with the inflaton being the superpartner of the goldstino. We first show that charged matter fields can be consistently added with the new term, as well as the standard FI term in supergravity in a K\"ahler frame where the $U(1)$ is not an R-symmetry. We then show that the slow-roll conditions can be easily satisfied with inflation driven by a D-term depending on the two FI parameters. Inflation starts at initial conditions around the maximum of the potential where the $U(1)$ symmetry is restored and stops when the inflaton rolls down to the minimum describing the present phase of our Universe. The resulting tensor-to-scalar ratio of primordial perturbations can be even at observable values in the presence of higher order terms in the K\"ahler potential.

[203] arXiv:1803.03814v1 [pdf, vox]

Detecting higher spin fields through statistical anisotropy in the CMB bispectrum

Gabriele Franciolini, Alex Kehagias, Antonio Riotto, Maresuke Shiraishi
Submitted Saturday 10 March 2018 @ 14:24:16 GMT
11 pages, 5 figures

Inflation may provide a suitable collider to probe physics at very high energies. In this paper we investigate the impact on the CMB bispectrum of higher spin fields which are long-lived on super-Hubble scales, e.g. partially massless higher spin fields. We show that distinctive statistical anisotropic signals on the CMB three-point correlator are induced and we investigate their detectability.

[204] arXiv:1803.03812v1 [pdf, vox]

Exoplanet Diversity in the Era of Space-based Direct Imaging Missions

Ravi Kopparapu, Eric Hebrard, Rus Belikov, Natalie M. Batalha, Gijs D. Mulders, Chris Stark, Dillon Teal, Shawn Domagal-Goldman, Dawn Gelino, Avi Mandell, Aki Roberge, Stephen Rinehart, Stephen R. Kane, Yasuhiro Hasegawa, Wade Henning, Brian Hicks, Vardan Adibekyan, Edward W. Schwieterman, Erika Kohler, Johanna Teske, Natalie Hinkel, Conor Nixon, Kevin France, William Danchi, Jacob Haqq-Misra, Eric T. Wolf, Scott D. Guzewich, Benjamin Charnay, Giada Arney, Hilairy E. Hartnett, Eric D. Lopez, Dante Minniti, Joe Renaud, Vladimir Airapetian, Chuanfei Dong, Anthony D. Del Genio, Melissa Trainer, Gioia Rau, Adam Jensen, Michael Way, Carey M. Lisse, Wladimir Lyra, Franck Marchis, Daniel Jontof-Hutter, Patrick Young, Ray Pierrehumbert, Chester E. Harman, Jonathan Fortney, Bill Moore, Steven Beckwith, Everett Shock, Steve Desch, Kathleen E. Mandt, Noam Izenberg, Eric B. Ford, Shannon Curry, Caleb Scharf, Ariel Anbar
Submitted Saturday 10 March 2018 @ 14:18:37 GMT
A white paper submitted to the National Academy of Sciences Exoplanet Science Strategy

This whitepaper discusses the diversity of exoplanets that could be detected by future observations, so that comparative exoplanetology can be performed in the upcoming era of large space-based flagship missions. The primary focus will be on characterizing Earth-like worlds around Sun-like stars. However, we will also be able to characterize companion planets in the system simultaneously. This will not only provide a contextual picture with regards to our Solar system, but also presents a unique opportunity to observe size dependent planetary atmospheres at different orbital distances. We propose a preliminary scheme based on chemical behavior of gases and condensates in a planet's atmosphere that classifies them with respect to planetary radius and incident stellar flux.

[205] arXiv:1803.03798v1 [pdf, vox]

Vacuum birefringence and the X-ray polarization from black-hole accretion disks

Ilaria Caiazzo, Jeremy Heyl
Submitted Saturday 10 March 2018 @ 12:14:55 GMT
11 pages, 3 figures, submitted to PRD

In the next decade, X-ray polarimetry will open a new window on the high-energy Universe, as several missions that include an X-ray polarimeter are currently under development. Observations of the polarization of X-rays coming from the accretion disks of stellar-mass and supermassive black holes are among the new polarimeters' major objectives. In this paper, we show that these observations can be affected by the quantum electrodynamic (QED) effect of vacuum birefringence: after an X-ray photon is emitted from the accretion disk, its polarization changes as the photon travels through the accretion disk's magnetosphere, as a result of the vacuum becoming birefringent in presence of a magnetic field. We show that this effect can be important for black holes in the energy band of the upcoming polarimeters, and has to be taken into account in a complete model of the X-ray polarization that we expect to detect from black-holes accretion disks, both for stellar mass and for supermassive black holes. We find that, for a chaotic magnetic field in the disk, QED can significantly decrease the linear polarization fraction of edge-on photons, depending on the spin of the hole and on the strength of the magnetic field. This effect can provide, for the first time, a direct way to probe the magnetic field strength close to the innermost stable orbit of black-hole accretion disks and to study the role of magnetic fields in astrophysical accretion in general.

[206] arXiv:1803.03789v1 [pdf, vox]

Lyman-alpha emitters gone missing: the different evolution of the bright and faint populations

Lewis H. Weinberger, Girish Kulkarni, Martin G. Haehnelt, Tirthankar Roy Choudhury, Ewald Puchwein
Submitted Saturday 10 March 2018 @ 10:33:17 GMT
25 pages, 16 figures, 2 appendices; submitted to MNRAS. Comments welcome

We model the transmission of the Lyman-alpha line through the circum- and intergalactic media around dark matter haloes expected to host Lyman-alpha emitters (LAEs) at z > 5.7, using the high-dynamic-range Sherwood simulations. We find very different CGM environments around more massive haloes (~10^11 M_sun) compared to less massive haloes (~10^9 M_sun) at these redshifts, which can contribute to a different evolution of the Lyman-alpha transmission from LAEs within these haloes. Additionally we confirm that part of the differential evolution could result from bright LAEs being more likely to reside in larger ionized regions. We conclude that a combination of the CGM environment and the IGM ionization structure is likely to be responsible for the differential evolution of the bright and faint ends of the LAE luminosity function at z > 6. More generally, we confirm the suggestion that the self-shielded neutral gas in the outskirts of the host halo can strongly attenuate the Lyman-alpha emission from high redshift galaxies. We find that this has a stronger effect on the more massive haloes hosting brighter LAEs. The faint-end of the LAE luminosity function is thus a more reliable probe of the average ionization state of the IGM. Comparing our model for LAEs with a range of observational data we find that the favoured reionization histories are our previously advocated `Late' and `Very Late' reionization histories, in which reionization finishes rather rapidly at around z ~ 6.

[207] arXiv:1803.03781v1 [pdf, vox]

The lamppost model: effects of photon trapping, the bottom lamp and disc truncation

Andrzej Niedzwiecki, Andrzej A. Zdziarski
Submitted Saturday 10 March 2018 @ 09:04:31 GMT
submitted to MNRAS

We study the lamppost model, in which the primary X-ray sources in accreting black-hole systems are located symmetrically on the rotation axis on both sides of the black hole surrounded by an accretion disc. We show the importance of the emission of the source on the opposite side to the observer. Due to gravitational light bending, its emission can increase the direct (i.e., not re-emitted by the disc) flux by as much as an order of magnitude. This happens for near to face-on observers when the disc is even moderately truncated. For truncated discs, we also consider effects of emission of the top source gravitationally bent around the black hole. We also present results for the attenuation of the observed radiation with respect to that emitted by the lamppost as functions of the lamppost height, black-hole spin and the degree of disc truncation. This attenuation, which is due to the time dilation, gravitational redshift and the loss of photons crossing the black-hole horizon, can be as severe as by several orders of magnitude for low lamppost heights. We also consider the contribution to the observed flux due to re-emission by optically-thick matter within the innermost stable circular orbit.

[208] arXiv:1803.03775v1 [pdf, vox]

Light scattering by fractal dust aggregates II: Opacity and asymmetry parameter

Ryo Tazaki, Hidekazu Tanaka
Submitted Saturday 10 March 2018 @ 08:23:37 GMT
22 pages, 11 figures; submitted to ApJ

Optical properties of dust aggregates become important at various astrophysical environments. To find a reliable approximation method for optical properties of dust aggregates, we calculate the opacity and the asymmetry parameter of dust aggregates by using a rigorous numerical method, the T-Matrix Method (TMM), and then the results are compared to those obtained by approximate methods; the Rayleigh--Gans--Deby​e (RGD) theory, the effective medium theory (EMT), and the distribution of hollow spheres method (DHS). First of all, we confirm that the RGD theory breaks down when multiple scattering becomes important. In addition, we find that both EMT and DHS fail to reproduce the optical properties of dust aggregates with fractal dimension of 2 when the incident wavelength is shorter than the aggregate radius. In order to solve these problems, we test the mean field theory (MFT), where multiple scattering can be taken into account. We show that the extinction opacity of dust aggregates can be well reproduced by MFT. However, it is also shown that once multiple scattering becomes important, MFT is not able to reproduce the scattering and absorption opacities. We successfully resolve this weak point of MFT, by newly developing a modified mean field theory (MMF). Hence, we conclude that MMF can be a useful tool to investigate radiative transfer properties of various astrophysical environments. We also discuss an enhancement of the absorption opacity of dust aggregates in the Rayleigh domain, which would be important to explain the large millimeter-wave opacity inferred from observations of protoplanetary disks.

[209] arXiv:1803.03751v1 [pdf, vox]

Exploring Extreme Space Weather Factors of Exoplanetary Habitability

V. S. Airapetian, V. Adibekyan, M. Ansdell, O. Cohen, M. Cuntz, W. Danchi, C. F. Dong, J. J. Drake, A. Fahrenbach, K. France, K. Garcia-Sage, A. Glocer, J. L. Grenfell, G. Gronoff, H. Hartnett, W. Henning, N. R. Hinkel, A. G. Jensen, M. Jin, P. Kalas, S. R. Kane, K. Kobayashi, R. Kopparapu, J. Leake, M. López-Puertas, T. Lueftinger, B. Lynch, W. Lyra, A. M. Mandell, K. E. Mandt, W. B. Moore, D. Nna-Mvondo, Y. Notsu, H. Maehara, Y. Yamashiki, K. Shibata, L. D. Oman, R. A. Osten, A. Pavlov, R. M. Ramirez, S. Rugheimer, J. E. Schlieder, J. D. Schnittman, E. L. Shock, C. Sousa-Silva, M. J. Way, Y. Yang, P. A. Young, G. P. Zank
Submitted Saturday 10 March 2018 @ 03:54:52 GMT
6 pages, the white paper submitted to the US National Academy of Sciences call on Exoplanet Science Strategy

It is currently unknown how common life is on exoplanets, or how long planets can remain viable for life. To date, we have a superficial notion of habitability, a necessary first step, but so far lacking an understanding of the detailed interaction between stars and planets over geological timescales, dynamical evolution of planetary systems, and atmospheric evolution on planets in other systems. A planet mass, net insolation, and atmospheric composition alone are insufficient to determine the probability that life on a planet could arise or be detected. The latter set of planetary considerations, among others, underpin the concept of the habitable zone (HZ), defined as the circumstellar region where standing bodies of liquid water could be supported on the surface of a rocky planet. However, stars within the same spectral class are often treated in the same way in HZ studies, without any regard for variations in activity among individual stars. Such formulations ignore differences in how nonthermal emission and magnetic energy of transient events in different stars affect the ability of an exoplanet to retain its atmosphere.In the last few years there has been a growing appreciation that the atmospheric chemistry, and even retention of an atmosphere in many cases, depends critically on the high-energy radiation and particle environments around these stars. Indeed, recent studies have shown stellar activity and the extreme space weather, such as that created by the frequent flares and coronal mass ejections (CMEs) from the active stars and young Sun, may have profoundly affected the chemistry and climate and thus habitability of the early Earth and terrestrial type exoplanets. The goal of this white paper is to identify and describe promising key research goals to aid the field of the exoplanetary habitability for the next 20 years.

[210] arXiv:1803.03732v1 [pdf, vox]

Precision Space Astrometry as a Tool to Find Earth-like Exoplanets

Michael Shao, Slava G. Turyshev, Eduardo Bendek, Debra Fischer, Olivier Guyon, Barbara McArthur, Matthew Muterspaugh, Chengxing Zhai, Celine Boehm
Submitted Saturday 10 March 2018 @ 01:10:51 GMT
A White Paper to the National Academy of Sciences Committee on an Exoplanet Science Strategy Call for Papers. 6 pages, 2 figures, 1 table

Because of the recent technological advances, the key technologies needed for precision space optical astrometry are now in hand. The Microarcsecond Astrometry Probe (MAP) mission concept is designed to find 1 Earth mass planets at 1AU orbit (scaled to solar luminosity) around the nearest ~90 FGK stars. The MAP payload includes i) a single three-mirror anastigmatic telescope with a 1-m primary mirror and metrology subsystems, and ii) a camera. The camera focal plane consists of 42 detectors, providing a Nyquist sampled FOV of 0.4-deg. Its metrology subsystems ensure that MAP can achieve the 0.8 uas astrometric precision in 1 hr, which is required to detect Earth-like exoplanets in our stellar neighborhood. MAP mission could provide ~10 specific targets for a much larger coronagraphic mission that would measure its spectra. We argue for the development of the space astrometric missions capable of finding Earth-2.0. Given the current technology readiness such missions relying on precision astrometry could be flown in the next decade, perhaps in collaboration with other national space agencies.

[211] arXiv:1803.03730v1 [pdf, vox]

A White Paper Submitted to The National Academy of Science's Committee on Exoplanet Science Strategy: Observing Exoplanets with the James Webb Space Telescope

Charles A. Beichman, Tom P. Greene
Submitted Saturday 10 March 2018 @ 00:48:23 GMT
White Paper submitted to NAS Exoplanet Strategy Committee

The James Webb Space Telescope (JWST) will revolutionize our understanding of exoplanets with transit spectroscopy of a wide range of mature planets close to their host stars ($<$2 AU) and with coronagraphic imaging and spectroscopy of young objects located further out ($>$10 AU). The census of exoplanets has revealed an enormous variety of planets orbiting stars of all ages and spectral types. With TESS adding to this census with its all-sky survey of the closest, brightest stars, the challenge of the coming decade will be to move from demography to physical characterization. This white paper discusses the wide variety of exoplanet opportunities enabled by JWST's sensitivity and stability, its high angular resolution, and its suite of powerful instruments. JWST observations will advance our understanding of the atmospheres of young to mature planets and will provide new insights into planet formation.

Submitted Fri, 09 Mar 2018

[212] arXiv:1803.03693v1 [pdf, vox]

Laboratory Measurements of X-Ray Emission from Highly Charged Argon Ions

Esra Bulbul, Adam Foster, Gregory V. Brown, Mark W. Bautz, Peter Beiersdorfer, Natalie Hell, Caroline Kilbourne, Ralph Kraft, Richard Kelley, Maurice A. Leutenegger, Eric D. Miller, F. Scott Porter, Randall K. Smith
Submitted Friday 09 March 2018 @ 21:03:33 GMT
Submitted to ApJ. 9 pages, 4 figures

Uncertainties in atomic models will introduce noticeable additional systematics in calculating the flux of weak dielectronic recombination (DR) satellite lines, affecting the detection and flux measurements of other weak spectral lines. One important example is the Ar XVII He-beta DR, which is expected to be present in emission from the hot intracluster medium of galaxy clusters and impacts measurements of the flux of the 3.5 keV line that has been suggested as a secondary emission from a dark matter interaction. To test the atomic models, we used the Lawrence Livermore National Laboratory's EBIT-I electron beam ion trap and the X-Ray Spectrometer quantum calorimeter XRS/EBIT, whose energy resolution is 5 eV, to measure the X-ray emission following resonant DR onto helium-like and lithium-like Argon. The measurements were completed using EBIT-I's Maxwellian simulator mode at a simulated electron temperature of Te=1.7 keV, similar to the plasma temperature observed in clusters of galaxies. We find that the measured summed flux of the Ar XVII He-beta DR line relative to the Ar XVI He-beta is underestimated by a factor of 2.3 in the atomic models of AtomDB v3.0.8 and previous versions. Although a substantial difference, it does not affect the results of Bulbul et al. (2014a) as they included a factor of three variance when determining the flux of the 3.5 keV line to account for potential uncertainties related to atomic models. As part of this study, a number of weak lines in the 3.5-3.6 keV band were identified from transitions not included in the original model. Once included however, the flux from these lines still does not account for the flux in the 3.5 keV line assuming reasonable plasma parameters. Therefore, the possible Ar XVII He-beta DR origin of the line mentioned in Bulbul et al. (2014a) can be excluded. (Abridged).

[213] arXiv:1803.03691v1 [pdf, vox]

Cascades and Dissipative Anomalies in Nearly Collisionless Plasma Turbulence

Gregory L. Eyink
Submitted Friday 09 March 2018 @ 20:52:07 GMT

We develop first-principles theory of kinetic plasma turbulence governed by the Vlasov-Maxwell-Landa​u equations in the limit of vanishing collision rates. Following an exact renormalization-grou​p approach pioneered by Onsager, we demonstrate the existence of a "collisionless range" of scales (lengths and velocities) in 1-particle phase space where the ideal Vlasov-Maxwell equations are satisfied in a "coarse-grained sense". Entropy conservation may nevertheless be violated in that range by a "dissipative anomaly" due to nonlinear entropy cascade. We derive "4/5th-law" type expressions for the entropy flux, which allow us to characterize the singularities (structure-function scaling exponents) required for its non-vanishing. Conservation laws of mass, momentum and energy are not afflicted with anomalous transfers in the collisionless limit. In a subsequent limit of small gyroradii, however, anomalous contributions to inertial-range energy balance may appear due both to cascade of bulk energy and to turbulent redistribution of internal energy in phase space. In that same limit the "generalized Ohm's law" derived from the particle momentum balances reduces to an "ideal Ohm's law", but only in a coarse-grained sense that does not imply magnetic flux-freezing and that permits magnetic reconnection at all inertial-range scales. We compare our results with prior theory based on the gyrokinetic (high gyro-frequency) limit, with numerical simulations, and with spacecraft measurements of the solar wind and terrestrial magnetosphere.

[214] arXiv:1803.03678v1 [pdf, vox]

Early-type galaxies in the Antlia Cluster: Catalogue and isophotal analysis

Juan P. Calderón, Lilia P. Bassino, Sergio A. Cellone, Matías Gómez
Submitted Friday 09 March 2018 @ 20:06:31 GMT
Accepted for publication in MNRAS

We present a statistical isophotal analysis of 138 early-type galaxies in the Antlia cluster, located at a distance of ${\sim} 35$ Mpc. The observational material consists of CCD images of four $36$ arcmin ${\times} 36$ arcmin fields obtained with the MOSAIC II camera at the Blanco 4-m telescope at CTIO. Our present work supersedes previous Antlia studies in the sense that the covered area is four times larger, the limiting magnitude is $M_{B} {\sim} -9.6$ mag, and the surface photometry parameters of each galaxy are derived from S\'ersic model fits extrapolated to infinity. In a companion previous study we focused on the scaling relations obtained by means of surface photometry, and now we present the data, on which the previous paper is based, the parameters of the isophotal fits as well as an isophotal analysis. For each galaxy, we derive isophotal shape parameters along the semi-major axis and search for correlations within different radial bins. Through extensive statistical tests, we also analyse the behaviour of these values against photometric and global parameters of the galaxies themselves. While some galaxies do display radial gradients in their ellipticity (${\epsilon}$) and/or their Fourier coefficients, differences in mean values between adjacent regions are not statistically significant. Regarding Fourier coefficients, dwarf galaxies usually display gradients between all adjacent regions, while non-dwarfs tend to show this behaviour just between the two outermost regions. Globally, there is no obvious correlation between Fourier coefficients and luminosity for the whole magnitude range ($-12 {\gtrsim} M_{V} {\gtrsim} -22$); however, dwarfs display much higher dispersions at all radii.

[215] arXiv:1803.03675v1 [pdf, vox]

Active Galactic Nuclei Feedback in an Elliptical Galaxy with the Most Updated AGN Physics (II): High-Angular Momentum Case

Doosoo Yoon, Feng Yuan, Zhao-Ming Gan, Jeremiah P. Ostriker, Ya-Ping Li, Luca Ciotti
Submitted Friday 09 March 2018 @ 19:48:50 GMT
18 pages, 14 figures, submitted to ApJ

This is the second paper of our series to study the effects of active galactic nuclei (AGN) feedback on the cosmological evolution of an isolated elliptical galaxy by performing two-dimensional high-resolution hydrodynamical numerical simulations. In these simulations, the inner boundary of the simulation is chosen so that the Bondi radius is resolved. Physical processes like star formation, Type Ia and Type II supernovae are taken into account. Compared to previous works, the main improvements is that we adopt the most updated AGN physics, which is described in detail in the first paper of this series (Yuan et al. 2017, Paper I). These improvements include the discrimination of the two accretion modes of the central AGN and the most updated descriptions of the wind and radiation in the two modes. In Paper I, we consider the case that the specific angular momentum of the gas in the galaxy is very low. In this paper, we consider the case where the specific angular momentum of the gas in the galaxy is significantly higher. In such a large spatial scale, it is believed that some mechanisms such as asymmetric gravitational torques, plays the role of angular momentum transport. We make use of the $\alpha$-prescriptio​n to mimic such a mechanism. Same as Paper I, we investigate the AGN light curve, typical AGN lifetime, growth of the black hole mass, AGN duty-cycle, star formation, and the X-ray surface brightness of the galaxy. Especially, we focus on the effects of specific angular momentum of the galaxy on these properties. We find that some results are qualitatively similar to those shown in Paper I, some results such as star formation and black hole growth do show a significant difference due to the mass concentration in the galactic disk as a consequence of galactic rotation.

[216] arXiv:1803.03661v1 [pdf, vox]

Competition between delta isobars and hyperons and properties of compact stars

Jia Jie Li, Armen Sedrakian, Fridolin Weber
Submitted Friday 09 March 2018 @ 19:15:07 GMT
7 pages, 4 figures

The $\Delta$-isobar degrees of freedom are included in the covariant density functional (CDF) theory to study the equation of state (EoS) and composition of dense matter in compact stars. In addition to $\Delta$'s we include the full octet of baryons, which allows us to study the interplay between the onset of delta isobars and hyperonic degrees of freedom. Using both the Hartree and Hartree-Fock approximation we find that $\Delta$'s appear already at densities slightly above the saturation density of nuclear matter for a wide range of the meson-$\Delta$ coupling constants. This delays the appearance of hyperons and significantly affects the gross properties of compact stars. Specifically, $\Delta$'s soften the EoS at low densities but stiffen it at high densities. This softening reduces the radius of a canonical $1.4 M_\odot$ star by up to 2~km for a reasonably attractive $\Delta$ potential in matter, while the stiffening results in larger maximum masses of compact stars. We conclude that the hypernuclear CDF parametrizations that satisfy the 2$M_\odot$ maximum mass constraint remain valid when $\Delta$ isobars are included, with the important difference that the resulting stellar radii are shifted toward lower values, which is in agreement with the analysis of neutron star radii.

[217] arXiv:1803.03655v1 [pdf, vox]

Accurately predicting the escape fraction of ionizing photons using restframe ultraviolet absorption lines

J. Chisholm, S. Gazagnes, D. Schaerer, A. Verhamme, J. R. Rigby, M. Bayliss, K. Sharon, M. Gladders, H. Dahle
Submitted Friday 09 March 2018 @ 19:01:28 GMT
12 pages, 5 figures. Resubmitted to A&A. Comments welcome

The fraction of ionizing photons that escape high-redshift galaxies sensitively determines whether galaxies reionized the early universe. However, this escape fraction cannot be measured from high-redshift galaxies because the opacity of the intergalactic medium is large at high-redshifts. Without methods to indirectly measure the escape fraction of high-redshift galaxies, it is unlikely that we will know what reionized the universe. Here, we analyze the far-ultraviolet H I (Lyman series) and low-ionization metal absorption lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use the H I covering fractions, column densities, and dust attenuations measured in a companion paper to predict the escape fraction of ionizing photons. We find good agreement between the predicted and observed Lyman continuum escape fractions (within $1.4\sigma$) using both the H I and the Si II absorption lines. The ionizing photons escape through holes in the H I, but we show that dust attenuation reduces the fraction of photons that escape galaxies. This means that the average high-redshift galaxy likely emits more ionizing photons than low-redshift galaxies. Two other indirect methods accurately predict the escape fractions: the Ly$\alpha$ escape fraction and the optical [O III]/[O II] flux ratio. We use these indirect methods to predict the escape fraction of a sample of 21 galaxies with rest-frame ultraviolet spectra but without Lyman continuum observations. Many of these galaxies have low escape fractions ($f_\text{esc}\le 1$%), but eleven have escape fractions $>1$%. The methods presented here will measure the escape fractions of high-redshift galaxies, enabling future telescopes to determine whether star-forming galaxies reionized the early universe.

[218] arXiv:1803.03653v1 [pdf, vox]

Spectroscopic decomposition of NGC 3521: unveiling the properties of the bulge and disc

Lodovico Coccato, Maximilian H. Fabricius, Roberto P. Saglia, Ralf Bender, Peter Erwin, Niv Drory, Lorenzo Morelli
Submitted Friday 09 March 2018 @ 19:00:05 GMT
13 pages, 11 figures, accepted for publication in MNRAS

We study the kinematics and the stellar populations of the bulge and disc of the spiral galaxy NGC 3521. At each position in the field of view, we separate the contributions of the bulge and the disc from the total observed spectrum and study their kinematics, age, and metallicities independently. Their properties are clearly distinct: the bulge rotates more slowly, has a higher velocity dispersion, and is less luminous than the disc. We identify three main populations of stars in NGC 3521: old ($\geq7$ Gyr), intermediate ($\approx$ 3 Gyr), and young ($\leq$1 Gyr). The mass and light of NGC 3521 are dominated by the intermediate stellar population. The youngest population contributes mostly to the disc component and its contribution increases with radius. We also study the luminosity-weighed properties of the stars in NGC 3521. Along the photometric major axis, we find: i) no age gradient for the stars in the bulge, and a negative age gradient for the stars in the disc; ii) negative metallicity gradients and sub-solar $\alpha$-enhancement for both the bulge and the disc. We propose the following picture for the formation of NGC 3521: initial formation a long time ago ($\geq 7$ Gyr), followed by a second burst of star formation or a merger ($\approx$ 3 Gyrs ago), which contributed predominantly to the mass-build up of the bulge. Recently ($\leq 1$ Gyr), the disc of NGC 3521 experienced an additional episode of star formation that started in the innermost regions.

[219] arXiv:1803.03652v1 [pdf, vox]

SPH to Grid: a new integral conserving method

Bernhard Röttgers, Alexander Arth
Submitted Friday 09 March 2018 @ 19:00:04 GMT
14 pages, 7 figures, 1 table Submitted to Astronomy & Computing

Analysing data from Smoothed Particle Hydrodynamics (SPH) simulations is about understanding global fluid properties rather than individual fluid elements. Therefore, in order to properly understand the outcome of such simulations it is crucial to transition from a particle to a grid based picture. In this paper we briefly summarise different methods of calculating a representative volume discretisation from SPH data and propose an improved version of commonly used techniques. We present a possibility to generate accurate 2D data directly without the CPU time and memory consuming detour over a 3D grid. We lay out the importance of an accurate algorithm to conserve integral fluid properties and to properly treat small scale structures using a typical galaxy simulation snapshot. For demonstration purposes we additionally calculate velocity power spectra and as expected find the main differences on small scales. Finally we propose two new multi-purpose analysis packages which utilise the new algorithms: Pygad and SPHMapper.

[220] arXiv:1803.03649v1 [pdf, vox]

Unsqueezing of standing waves due to inflationary domain structure

Carlo R. Contaldi, Joao Magueijo
Submitted Friday 09 March 2018 @ 19:00:01 GMT

The so-called "trans-Planckian" problem of inflation may be evaded by positing that modes come into existence only when they became "cis-Planckian" by virtue of expansion. However, this would imply that for any mode a new random realization would have to be drawn every $N$ wavelengths, with $N$ typically of order 1000 (but it could be larger or smaller). Such a re-drawing of realizations leads to a heteroskodastic distribution if the region under observation contains several such independent domains. This has no effect on the sampled power spectrum for a scale-invariant raw spectrum, but at very small scales it leads to a spectral index bias towards scale-invariance and smooths oscillations in the spectrum. The domain structure would also "unsqueeze" some of the propagating waves, i.e., dismantle their standing wave character. By describing standing waves as travelling waves of the same amplitude moving in opposite directions we determine the observational effects of unsqueezing. We find that it would erase the Doppler peaks in the CMB, but only on very small angular scales, where the primordial signal may not be readily accessible. The standing waves in a primordial gravitational wave background would also be turned into travelling waves. This unsqueezing of the gravitational wave background may constitute a detectable phenomenon.

[221] arXiv:1803.03644v1 [pdf, vox]

Converting non-relativistic dark matter to radiation

Torsten Bringmann, Felix Kahlhoefer, Kai Schmidt-Hoberg, Parampreet Walia
Submitted Friday 09 March 2018 @ 19:00:00 GMT
21 pages revtex4, 14 figures

Dark matter in the cosmological concordance model is parameterised by a single number, describing the covariantly conserved energy density of a non-relativistic fluid. Here we test this assumption in a model-independent and conservative way by considering the possibility that, at any point during the cosmological evolution, dark matter may be converted into a non-interacting form of radiation. This scenario encompasses, but is more general than, the cases where dark matter decays or annihilates into these states. We show that observations of the cosmic microwave background allow to strongly constrain this scenario for all conversion times after big bang nucleosynthesis. We discuss in detail, both from a Bayesian and frequentist point of view, in which sense adding large-scale structure observations may even provide a certain preference for a conversion of dark matter to radiation at late times. Finally we apply our general results to a specific particle physics realisation of such a scenario, featuring late kinetic decoupling and Sommerfeld-enhanced dark matter annihilation. We identify a small part of parameter space that both mitigates the tension between cosmic microwave and large-scale structure data and allows for velocity-dependent dark matter self-interactions strong enough to address the small-scale problems of structure formation.

[222] arXiv:1803.03646v1 [pdf, vox]

Aspherical Supernovae: Effects on Early Light Curves

Niloufar Afsariardchi, Christopher D. Matzner
Submitted Friday 09 March 2018 @ 19:00:00 GMT
23 pages, 20 figures, Accepted for publication in ApJ

Early light from core-collapse supernovae, now detectable in high-cadence surveys, holds clues to a star and its environment just before it explodes. However, effects that alter the early light have not been fully explored. We highlight the possibility of non-radial flows at the time of shock breakout. These develop in sufficiently non-spherical explosions if the progenitor is not too diffuse. When they do develop, non-radial flows limit ejecta speeds and cause ejecta-ejecta collisions. We explore these phenomena and their observational implications, using global, axisymmetric, non-relativistic FLASH simulations of simplified polytropic progenitors, which we scale to representative stars. We develop a method to track photon production within the ejecta, enabling us to estimate band-dependent light curves from adiabatic simulations. Immediate breakout emission becomes hidden as an oblique flow develops. Non-spherical effects lead the shock-heated ejecta to release a more constant luminosity at a higher, evolving color temperature at early times, effectively mixing breakout light with the early light curve. Collisions between non-radial ejecta thermalize a small fraction of the explosion energy; we address emission from these collisions in a subsequent paper.

[223] arXiv:1803.03648v1 [pdf, vox]

Inner Super-Earths, Outer Gas Giants: How Pebble Isolation and Migration Feedback Keep Jupiters Cold

Jeffrey Fung, Eve Lee
Submitted Friday 09 March 2018 @ 19:00:00 GMT
Submitted to AAS Journals

The majority of gas giants (planets of masses $\gtrsim10^2 M_\oplus$) are found to reside at distances beyond $\sim1$ au from their host stars. Within 1 au, the planetary population is dominated by super-Earths of $2-20 M_\oplus$. We show that this dichotomy between inner super-Earths and outer gas giants can be naturally explained should they form in nearly inviscid disks. In laminar disks, a planet can more easily repel disk gas away from its orbit. The feedback torque from the pile-up of gas inside the planet's orbit slows down and eventually halts migration. A pressure bump outside the planet's orbit traps pebbles and solids, starving the core. Gas giants are born cold and stay cold: more massive cores are preferentially formed at larger distances, and they barely migrate under disk feedback. We demonstrate this using 2D hydrodynamical simulations of disk-planet interaction lasting up to $10^5$ years: we track planet migration and pebble accretion until both come to an end by disk feedback. Whether cores undergo runaway gas accretion to become gas giants or not is determined by computing 1D gas accretion models. Our simulations show that in an inviscid minimum mass solar nebula, gas giants do not form inside $\sim$0.5 au, nor can they migrate there while the disk is present. We also explore the dependence on disk mass, and find that gas giants form further out in less massive disks.

[224] arXiv:1803.03638v1 [pdf, vox]

On the Numerical Robustness of the Streaming Instability: Particle Concentration and Gas Dynamics in Protoplanetary Disks

Rixin Li, Andrew N. Youdin, Jacob B. Simon
Submitted Friday 09 March 2018 @ 18:59:41 GMT
19 pages, 13 figures, submitted to ApJ

The Streaming Instability (SI) is a mechanism to concentrate dust aerodynamically in protoplanetary disks. Simulations have shown that nonlinear particle clumping from the SI can trigger gravitational collapse into planetesimals. To better understand the numerical robustness of the SI, we perform a suite of vertically-stratifie​d 3D simulations with fixed physical parameters known to produce strong clumping. We test the effect of numerical parameters by varying the computational domain size and the vertical boundary conditions (vBCs), comparing a new implementation of outflow vBCs to the previously-used periodic and reflecting vBCs. We find the main effect of the SI - strongly nonlinear particle clumping - is mostly independent of the vBCs. However, the SI concentrates solids to higher peak densities in larger simulation domains due to a larger particle mass reservoir. We report that the SI triggers azimuthally-banded radial variations of gas pressure, known as zonal flows. They are never strong enough to halt particle radial drift in our simulations, confirming that particle trapping in gas pressure maxima is not the mechanism of the SI. We find that the outflow vBCs produce artificially large gas outflow rates at vertical boundaries. However, the outflow vBCs significantly reduce artificial reflections at vertical boundaries, thereby allowing particles to sediment into a thinner and less corrugated midplane layer, which converges better with box size. The radial spacing of dense particle filaments is ~0.15 of a gas scale height (H) for all vBCs, which sets the feeding zone for planetesimal growth in self-gravitating simulations. Our results thus validate the use of the outflow vBCs in SI simulations, despite the close proximity (<= 0.4H) of vertical boundaries to the disk midplane. Overall, our study demonstrates the numerical robustness of nonlinear particle clumping by the SI.

[225] arXiv:1803.03629v1 [pdf, vox]

Bounds on Dark Matter annihilations from 21 cm data

Guido D'Amico, Paolo Panci, Alessandro Strumia
Submitted Friday 09 March 2018 @ 18:31:11 GMT
6 pages

The observation of an absorption feature in the 21 cm spectrum at redshift $z\approx 17$ implies bounds on Dark Matter annihilations for a broad range of masses, given that significant heating of the intergalactic medium would have erased such feature. The resulting bounds on the DM annihilation cross sections are comparable to the strongest ones from all other observables.

[226] arXiv:1803.03625v1 [pdf, vox]

A Gemini view of the galaxy cluster RXC J1504-0248: insights on the nature of the central gaseous filaments

Ana Cecília Soja, Laerte Sodré Jr, Rogério Monteiro-Oliveira, Eduardo Serra Cypriano, Gastão Lima Neto
Submitted Friday 09 March 2018 @ 18:25:11 GMT
13 pages, 12 figures - Accepted for publication in MNRAS in 2018 March 07

We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift ($z = 0.216$). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining $M_{200} = 5.3\pm0.4 \times 10^{14}$ $h_{70}^{-1}$ M$_\odot$ within $R_{200} = 1.56 \pm 0.04$ $h^{-1}_{70}$ Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated to its BCG, located mainly along its major axis and aligned with the X-ray emission. A combined study of three emission line diagnostic diagrams has shown that the filament emission falls in the so-called transition region of these diagrams. Consequently, several ionizing sources should be playing an meaningful role. We have argued that old stars, often invoked to explain LINER emission, should not be the major source of ionization. We have noticed that most of the filamentary emission has line ratios consistent with the shock excitation limits obtained from shock models. We also found that line fluxes are related to gas velocities (here estimated from line widths) by power-laws with slopes in the range expected from shock models. These models also show, however, that only ~10% of H$\alpha$ luminosity can be explained by shocks. We conclude that shocks probably associated to the cooling of the intracluster gas in a filamentary structure may indeed be contributing to the filament nebular emission, but can not be the major source of ionizing photons.

[227] arXiv:1803.03624v1 [pdf, vox]

The usability of the optical parametric amplification of light for high-angular-resolut​ion imaging and fast astrometry

A. R. Kurek, A. Stachowski, K. Banaszek, A. Pollo
Submitted Friday 09 March 2018 @ 18:18:27 GMT
Received: 11 November 2017, revision received: 31 January 2018, accepted: 31 January 2018

High-angular-resolut​ion imaging is crucial for many applications in modern astronomy and astrophysics. The fundamental diffraction limit constrains the resolving power of both ground-based and spaceborne telescopes. The recent idea of a quantum telescope based on the optical parametric amplification (OPA) of light aims to bypass this limit for the imaging of extended sources by an order of magnitude or more. We present an updated scheme of an OPA-based device and a more accurate model of the signal amplification by such a device. The semiclassical model that we present predicts that the noise in such a system will form so-called light speckles as a result of light interference in the optical path. Based on this model, we analysed the efficiency of OPA in increasing the angular resolution of the imaging of extended targets and the precise localization of a distant point source. According to our new model, OPA offers a gain in resolved imaging in comparison to classical optics. For a given time-span, we found that OPA can be more efficient in localizing a single distant point source than classical telescopes.

[228] arXiv:1803.03619v1 [pdf, vox]

Signature of non-isotropic distribution of stellar rotation inclination angles in the Praesepe cluster

Geza Kovacs
Submitted Friday 09 March 2018 @ 17:53:43 GMT
Accepted for publication in Astronomy & Astrophysics: 5 pages with 4 figures

The distribution of the stellar rotation axes of 113 main sequence stars in the open cluster Praesepe are examined by using current photometric rotation periods, spectroscopic rotation velocities, and estimated stellar radii. Three different samples of stellar rotation data on spotted stars from the Galactic field and two independent samples of planetary hosts are used as control samples to support the consistency of the analysis. Considering the high completeness of the Praesepe sample and the behavior of the control samples, we find that the main sequence F - K stars in this cluster are susceptible to rotational axis alignment. Using a cone model, the most likely inclination angle is 76+/-14 degrees with a half opening angle of 47+/-24 degrees. Non-isotropic distribution of the inclination angles is preferred over the isotropic distribution, except if the rotation velocities used in this work are systematically overestimated. We found no indication of this being the case on the basis of the currently available data.

[229] arXiv:1803.03615v1 [pdf, vox]

Lorentz violating Hořava-Lifshitz gravity in light of new data

Nils A. Nilsson, Ewa Czuchry
Submitted Friday 09 March 2018 @ 17:43:25 GMT
Prepared for submission to JCAP

We present new observational constraints on Lorentz violating Ho\v{r}ava-Lifshitz cosmological scenarios using an updated cosmological data set from Cosmic Microwave Background (Planck CMB), expansion rates of elliptical and lenticular galaxies, JLA compilation (Joint Light-Curve Analysis) data for Type Ia supernovae (SneIa), Baryon Acoustic Oscillations (BAO) and priors on the Hubble parameter. And a different parametrisation of the equations. Unlike in other approaches we consider the curvature parameter $\Omega_k$ as a free parameter in the analysis we considered the parameters $\Omega_k$ and $\Delta N_\nu$ as completely free, which helped to place new, updated bounds on several of the theory parameters. Remarkably, the detailed balance scenario exhibits negative spatial curvature to more than $3\sigma$, whereas for further theory generalizations we found evidence for positive spatial curvature at 1$\sigma$. This could create circumstantial evidence from observations and could be used to single out distinct formulations and scenarios.

[230] arXiv:1803.03604v1 [pdf, vox]

SDSS-IV MaNGA: The Spectroscopic Discovery of Strongly Lensed Galaxies

Michael S. Talbot, Joel R. Brownstein, Adam S. Bolton, Kevin Bundy, Brett H. Andrews, Brian Cherinka, Thomas E. Collett, Anupreeta More, Surhud More, Alessandro Sonnenfeld, Simona Vegetti, David A. Wake, Anne-Marie Weijmans, Kyle B. Westfall
Submitted Friday 09 March 2018 @ 17:16:14 GMT
Accepted for publication in MNRAS, March 8, 2018. In press. 16 pages, 5 figures, 4 tables

We present a catalogue of 38 spectroscopically detected strong galaxy-galaxy gravitational lens candidates identified in the Sloan Digital Sky Survey IV (SDSS-IV). We were able to simulate narrow-band images for 8 of them demonstrating evidence of multiple images. Two of our systems are compound lens candidates, each with 2 background source-planes. One of these compound systems shows clear lensing features in the narrow-band image. Our sample is based on 2812 galaxies observed by the Mapping Nearby Galaxies at APO (MaNGA) integral field unit (IFU). This Spectroscopic Identification of Lensing Objects (SILO) survey extends the methodology of the Sloan Lens ACS Survey (SLACS) and BOSS Emission-Line Survey (BELLS) to lower redshift and multiple IFU spectra. We searched ~ 1.5 million spectra, of which 3065 contained multiple high signal-to-noise background emission-lines or a resolved [OII] doublet, that are included in this catalogue. Upon manual inspection, we discovered regions with multiple spectra containing background emission-lines at the same redshift, providing evidence of a common source-plane geometry which was not possible in previous SLACS and BELLS discovery programs. We estimate more than half of our candidates have an Einstein radius > 1.7", which is significantly greater than seen in SLACS and BELLS. These larger Einstein radii produce more extended images of the background galaxy increasing the probability that a background emission-line will enter one of the IFU spectroscopic fibres, making detection more likely.

[231] arXiv:1803.03598v1 [pdf, vox]

Merging the Astrophysics and Planetary Science Information Systems

Michael J. Kurtz, Alberto Accomazzi, Edwin A. Henneken
Submitted Friday 09 March 2018 @ 17:05:18 GMT
Whitepaper submitted to the Committee on an Exoplanet Science Strategy

Conceptually exoplanet research has one foot in the discipline of Astrophysics and the other foot in Planetary Science. Research strategies for exoplanets will require efficient access to data and information from both realms. Astrophysics has a sophisticated, well integrated, distributed information system with archives and data centers which are interlinked with the technical literature via the Astrophysics Data System (ADS). The information system for Planetary Science does not have a central component linking the literature with the observational and theoretical data. Here we propose that the Committee on an Exoplanet Science Strategy recommend that this linkage be built, with the ADS playing the role in Planetary Science which it already plays in Astrophysics. This will require additional resources for the ADS, and the Planetary Data System (PDS), as well as other international collaborators

[232] arXiv:1803.03592v1 [pdf, vox]

Discovery of a radio nebula around PSR J0855-4644

C. Maitra, S. Roy, F. Acero, Y. Gupta
Submitted Friday 09 March 2018 @ 16:50:20 GMT
4 pages, 2 figures, accepted for publication in MNRAS Letters

We report the discovery of a diffuse radio emission around PSR J0855--4644 using an upgraded GMRT (uGMRT) observation at 1.35 GHz. The radio emission is spatially coincident with the diffuse X-ray pulsar wind nebula (PWN) seen with XMM but is much larger in extent compared to the compact axisymmetric PWN seen with Chandra. The morphology of the emission, with a bright partial ring-like structure and two faint tail-like features strongly resembles a bow shock nebula, and indicates a velocity of 100 km/s through the ambient medium. We conclude that the emission is most likely to be associated with the radio PWN of PSR J0855-4644. From the integrated flux density, we estimate the energetics of the PWN.

[233] arXiv:1803.02858v2 [pdf, vox]

Two warm, low-density sub-Jovian planets orbiting bright stars in K2 campaigns 13 and 14

Liang Yu, Joseph E. Rodriguez, Ian J. M. Crossfield, Jason D. Eastman, Avi Shporer, B. Scott Gaudi, Jennifer Burt, Benjamin J. Fulton, Evan Sinukoff, Andrew W. Howard, Howard Isaacson, Molly R. Kosiarek, David R. Ciardi, Joshua E. Schlieder, Kaloyan Penev, Andrew Vanderburg, Keivan G. Stassun, Allyson Bieryla, R. Paul Butler, Perry Berlind, Michael L. Calkins, Gilbert A. Esquerdo, David W. Latham, Gabriel Murawski, Daniel J. Stevens, Erik A. Petigura, Laura Kreidberg, Makennah Bristow
Submitted Friday 09 March 2018 @ 16:28:51 GMT
16 pages, 12 figures; submitted to AJ

We report the discovery of two planets transiting the bright stars HD 89345 (EPIC 248777106, V = 9.376, K = 7.721) in K2 Campaign 14 and HD 286123 (EPIC 247098361, V = 9.822, K = 8.434) in K2 Campaign 13. Both stars are G-type stars, one of which is at or near the end of its main sequence lifetime, and the other that is just over halfway through its main sequence lifetime. HD 89345 hosts a warm sub-Saturn (0.616 $R_J$, 0.103 $M_J$, $T_{eq}$ = 1059 K) in an 11.81-day orbit. The planet is similar in size to WASP-107b, which falls in the transition region between ice giants and gas giants. HD 286123 hosts a Jupiter-sized, low-mass planet (1.080 $R_J$, 0.408 $M_J$, $T_{eq}$ = 999 K) in an 11.17-day, mildly eccentric orbit, with $e = 0.268\pm 0.037$. Given that they orbit relatively evolved main-sequence stars with ages of ~5-7 Gyr, and have orbital periods longer than 10 days, these planets are interesting candidates for studies of gas planet evolution, migration, and (potentially) re-inflation. Both planets have spent their entire lifetimes near the proposed stellar irradiation threshold at which giant planets become inflated, and neither shows any sign of radius inflation. They probe the regime where inflation begins to become noticeable and are valuable in constraining planet inflation models. In addition, the brightness of the host stars, combined with large atmospheric scale heights of the planets, makes these two systems exceptionally favorable targets for transit spectroscopy to study their atmospheres and perhaps provide insight into the physical mechanisms that that lead to inflated hot Jupiters.

[234] arXiv:1803.03587v1 [pdf, vox]

The Green Bank Northern Celestial Cap Pulsar Survey II: The Discovery and Timing of Ten Pulsars

A. M. Kawash, M. A. McLaughlin, D. L. Kaplan, M. E. DeCesar, L. Levin, D. R. Lorimer, R. S. Lynch, K. Stovall, J. K. Swiggum, E. Fonseca, A. M. Archibald, S. Banaszak, C. M. Biwer, J. Boyles, B. Cui, L. P. Dartez, D. Day, S. Ernst, A. J. Ford, J. Flanigan, S. A. Heatherly, J. W. T. Hessels, J. Hinojosa, F. A. Jenet, C. Karako-Argaman, V. M. Kaspi, V. I. Kondratiev, S. Leake, G. Lunsford, J. G. Martinez, A. Mata, T. D. Matheny, A. E. Mcewen, M. G. Mingyar, A. L. Orsini, S. M. Ransom, M. S. E. Roberts, M. D. Rohr, X. Siemens, R. Spiewak, I. H. Stairs, J. van Leeuwen, A. N. Walker, B. L. Wells
Submitted Friday 09 March 2018 @ 16:26:32 GMT
9 pages, 5 figures

We present timing solutions for ten pulsars discovered in 350 MHz searches with the Green Bank Telescope. Nine of these were discovered in the Green Bank Northern Celestial Cap survey and one was discovered by students in the Pulsar Search Collaboratory program in analysis of drift-scan data. Following discovery and confirmation with the Green Bank Telescope, timing has yielded phase-connected solutions with high precision measurements of rotational and astrometric parameters. Eight of the pulsars are slow and isolated, including PSR J0930$-$2301, a pulsar with nulling fraction lower limit of $\sim$30\% and nulling timescale of seconds to minutes. This pulsar also shows evidence of mode changing. The remaining two pulsars have undergone recycling, accreting material from binary companions, resulting in higher spin frequencies. PSR J0557$-$2948 is an isolated, 44 \rm{ms} pulsar that has been partially recycled and is likely a former member of a binary system which was disrupted by a second supernova. The paucity of such so-called `disrupted binary pulsars' (DRPs) compared to double neutron star (DNS) binaries can be used to test current evolutionary scenarios, especially the kicks imparted on the neutron stars in the second supernova. There is some evidence that DRPs have larger space velocities, which could explain their small numbers. PSR J1806+2819 is a 15 \rm{ms} pulsar in a 44 day orbit with a low mass white dwarf companion. We did not detect the companion in archival optical data, indicating that it must be older than 1200 Myr.

[235] arXiv:1803.03584v1 [pdf, vox]

Pre-MAP Search for Transiting Objects Orbiting White Dwarfs

Aislynn Wallach, Brett M. Morris, Doug Branton, Teagan O'Reilly, Brittany Platt, Ada Beale, Andrew Yetter, Katie Reil, Kristen Garofali, Eric Agol
Submitted Friday 09 March 2018 @ 16:04:03 GMT
Accepted to RNAAS

Metal pollution in white dwarf atmospheres may be the accreted remnants of planetary objects. After the discovery of disintegrating planetary objects transiting WD 1145+017 (Vanderburg et al. 2015), undergraduates in the University of Washington's Pre- Major in Astronomy Program (Pre-MAP) were inspired to collect photometry of the brightest white dwarfs to hunt for similar transiting objects around other metal-polluted white dwarfs. Prior surveys have yet to make a detection of a transiting planet orbiting a white dwarf, yet white dwarfs are still an attractive target for searches of small, rocky planetary material. Since a typical white dwarf is Earth-sized, transits of Earth-sized planets could have depths >50%, so even low S/N photometry has a chance at discovering transiting material. We identified bright, northern, metal-polluted white dwarfs in the SDSS DR10 white dwarf catalog, and observed five targets with the Astrophysical Research Consortium Small Aperture Telescope (ARCSAT) 0.5-meter telescope at Apache Point Observatory. The ARCSAT photometry had sufficient precision to detect Moon-sized objects or larger at short orbital periods, though no such planets were detected for these targets. We look forward to surveys which may find planets orbiting white dwarfs, such as NASA's TESS, ESA's PLATO, and the Evryscope.

[236] arXiv:1803.03568v1 [pdf, vox]

The Mid-IR Albedo of Neptune Derived from Spitzer Observations

Anthony Mallama, Liming Li
Submitted Friday 09 March 2018 @ 15:39:08 GMT

Mid-IR albedo values of Neptune are derived from Spitzer Space Telescope measurements reported by Stauffer et al. (2016). The method of this derivation is described and the results indicate that the geometric albedo was about 1% or less at the time of the observations in 2016. Short-term mid-IR variability of Neptune, evidenced by the Spitzer observations themselves, indicates an albedo at 3.6 microns ranging from 0.2% to 0.6% with a mean of 0.4%. The corresponding albedos at 4.5 microns are 0.7%, 1.3% and 0.9%. Furthermore, the 60-year history of visible-light brightness variations, which show that Neptune was significantly fainter a few decades ago, suggests that the mid-IR albedo during that earlier period of time may have been much less than 1%. The albedo values reported here can have implications for models of Neptune's atmosphere. However, the mid-IR brightness of Neptune cannot contribute very strongly to its total albedo because the Sun emits only about 2% of its flux long-ward of 3 micron. By contrast, the Sun emits 42% of its flux at visible and near-UV wavelengths where the planet's albedo is in the tens of percents.

[237] arXiv:1803.03565v1 [pdf, vox]

On the potential of Cherenkov Telescope Arrays and KM3 Neutrino Telescopes for the detection of extended sources

Lucia Ambrogi, Silvia Celli, Felix Aharonian
Submitted Friday 09 March 2018 @ 15:34:57 GMT
15 pages, 7 figures

We discuss the discovery potential of extended very-high-energy (VHE) neutrino sources by the future KM3 Neutrino Telescope (KM3NeT) in the context of the constraining power of the Cherenkov Telescope Array (CTA), designed for deep surveys of the sky in VHE gamma rays. The study is based on a comparative analysis of sensitivities of KM3NeT and CTA. We show that a minimum gamma-ray energy flux of E^2{\phi}_{\gamma}(1​0 TeV) > 1x10^{-12} TeV cm^{-2} s^{-1} is required to identify a possible neutrino counterpart with a 3{\sigma} significance and 10 years of KM3NeT observations with upgoing muons, if the source has an angular size of R_{src} = 0.1 deg and emits gamma rays with an E^{-2} energy spectrum through a full hadronic mechanism. This minimum gamma-ray flux is increased to the level of E^2{\phi}_{\gamma}(1​0 TeV) > 2x10^{-11} TeV cm^{-2} s^{-1} in case of sources with radial extension of R_{src} = 2.0 deg. The analysis methods are applied to the supernova remnant RX J1713.7-3946 and the Galactic Center Ridge, as well as to the recent HAWC catalog of multi-TeV gamma-ray sources.

[238] arXiv:1803.03531v1 [pdf, vox]

Spatial variations of the Sr i 4607 Å scattering polarization peak

M. Bianda, S. Berdyugina, D. Gisler, R. Ramelli, L. Belluzzi, E. S. Carlin, J. O. Stenflo, T. Berkefeld
Submitted Friday 09 March 2018 @ 14:37:57 GMT
5 pages, 4 figures

Context. The scattering polarization signal observed in the photospheric Sr i 4607 {\AA} line is expected to vary at granular spatial scales. This variation can be due to changes in the magnetic field intensity and orientation (Hanle effect), but also to spatial and temporal variations in the plasma properties. Measuring the spatial variation of such polarization signal would allow us to study the properties of the magnetic fields at subgranular scales, but observations are challenging since both high spatial resolution and high spectropolarimetric sensitivity are required. Aims. We aim to provide observational evidence of the polarization peak spatial variations, and to analyze the correlation they might have with granulation. Methods. Observations conjugating high spatial resolution and high spectropolarimetric precision were performed with the Zurich IMaging POLarimeter, ZIMPOL, at the GREGOR solar telescope, taking advantage of the adaptive optics system and the newly installed image derotator. Results. Spatial variations of the scattering polarization in the Sr i 4607 {\AA} line are clearly observed. The spatial scale of these variations is comparable with the granular size. Small correlations between the polarization signal amplitude and the continuum intensity indicate that the polarization is higher at the center of granules than in the intergranular lanes.

[239] arXiv:1803.03517v1 [pdf, vox]

Axion energy density, bottle neck period, and $\barθ$ ratios between early and late times

Jihn E. Kim, Se-Jin Kim, Soonkeon Nam
Submitted Friday 09 March 2018 @ 14:15:41 GMT
11 pages with 5 figures

The possibility of the "invisible" axion being cold dark matter relies on the acceptable estimates of the current axion energy density. The estimate depends on the nature of QCD phase transition at a few hundred MeV and the evolution of the misalignment angle $\bar{\theta}$. The onset of $\bar{\theta}$ oscillation undergoes a bottleneck period which occurred during the QCD phase transition. In addition, the anharmonic coupling of order $a^4$ affects the $\bar{\theta}$ evolution. From the time that the anharmonic effect is negligible, it is rather simple to calculate the ratio of $\bar{\theta}$'s between early and late times. For multi GHz oscillations, the current age of the Universe needs at least $10^{27}$ oscillations which limits an exact calculation of $\bar{\theta}$ . We establish a stepwise approximation for numerical solutions of the differential equation and obtain $\bar{\theta}_{\rm now}/\bar{\theta}_f\​approx 3\times 10^{-17}$ for $m_a\simeq 10^{-4}\,$eV, where $t_f$ is the first time that the full hadronic phase (after the QCD phase transition) was established.

[240] arXiv:1803.03513v1 [pdf, vox]

Cosmic History and a Candidate Parent Asteroid for the Quasicrystal-bearing Meteorite Khatyrka

Matthias M. M. Meier, Luca Bindi, Philipp R. Heck, April I. Neander, Nicole H. Spring, My E. I. Riebe, Colin Maden, Heinrich Baur, Paul J. Steinhardt, Rainer Wieler, Henner Busemann
Submitted Friday 09 March 2018 @ 13:58:15 GMT
Submitted to Earth and Planetary Science Letters

The unique CV-type meteorite Khatyrka is the only natural sample in which "quasicrystals" and associated crystalline Cu,Al-alloys, including khatyrkite and cupalite, have been found. They are suspected to have formed in the early Solar System. To better understand the origin of these exotic phases, and the relationship of Khatyrka to other CV chondrites, we have measured He and Ne in six individual, ~40-{\mu}m-sized olivine grains from Khatyrka. We find a cosmic-ray exposure age of about 2-4 Ma (if the meteoroid was <3 m in diameter, more if it was larger). The U,Th-He ages of the olivine grains suggest that Khatyrka experienced a relatively recent (<600 Ma) shock event, which created pressure and temperature conditions sufficient to form both the quasicrystals and the high-pressure phases found in the meteorite. We propose that the parent body of Khatyrka is the large K-type asteroid 89 Julia, based on its peculiar, but matching reflectance spectrum, evidence for an impact/shock event within the last few 100 Ma (which formed the Julia family), and its location close to strong orbital resonances, so that the Khatyrka meteoroid could plausibly have reached Earth within its rather short cosmic-ray exposure age.

[241] arXiv:1803.03501v1 [pdf, vox]

Infall and Outflow Motions towards a Sample of Massive Star Forming Regions from the RMS Survey

Nichol Cunningham, Stuart Lumsden, Toby Moore, Luke Maud, Ignacio. Mendigutia
Submitted Friday 09 March 2018 @ 13:21:29 GMT
Accepted for publication in MNRAS

We present the results of an outflow and infall survey towards a distance limited sample of 31 massive star forming regions drawn from the RMS survey. The presence of young, active outflows is identified from SiO (8-7) emission and the infall dynamics are explored using HCO$^+$/H$^{13}$CO$^​+$ (4-3) emission. We investigate if the infall and outflow parameters vary with source properties, exploring whether regions hosting potentially young active outflows show similarities or differences with regions harbouring more evolved, possibly momentum driven, "fossil" outflows. SiO emission is detected towards approximately 46% of the sources. When considering sources with and without an SiO detection (i.e. potentially active and fossil outflows respectively), only the $^{12}$CO outflow velocity shows a significant difference between samples, indicating SiO is more prevalent towards sources with higher outflow velocities. Furthermore, we find the SiO luminosity increases as a function of the Herschel 70$\mu$m to WISE 22$\mu$m flux ratio, suggesting the production of SiO is prevalent in younger, more embedded regions. Similarly, we find tentative evidence that sources with an SiO detection have a smaller bolometric luminosity-to-mass ratio, indicating SiO (8-7) emission is associated with potentially younger regions. We do not find a prevalence towards sources displaying signatures of infall in our sample. However, the higher energy HCO$^+$ transitions may not be the best suited tracer of infall at this spatial resolution in these regions.

[242] arXiv:1803.02768v2 [pdf, vox]

Low frequency view of GW 170817/GRB 170817A with the Giant Meterwave Radio Telescope

L. Resmi, S. Schulze, C. H. Ishwara Chandra, K. Misra, J. Buchner, M. De Pasquale, R. Sanchez Ramirez, S. Klose, S. Kim, N. R. Tanvir, P. T. O'Brien
Submitted Friday 09 March 2018 @ 13:16:42 GMT
Submitted to the Astrophysical Journal, 5 figures, 2 tables, fixed typos in the title

The short gamma-ray burst (GRB) 170817A was the first GRB associated with a gravitational-wave event. Due to the exceptionally low luminosity of the prompt {\gamma}-ray and the afterglow emission, the origin of both radiation components is highly debated. The most discussed models for the burst and the afterglow include a regular GRB jet seen off-axis and the emission from the cocoon encompassing a "choked" jet. Here, we report low radio-frequency observations at 610 and 1390 MHz obtained with the Giant Metrewave Radio Telescope (GMRT). Our observations span a range of $\sim$ 7 to $\sim$ 152 days after the burst. The afterglow started to emerge at these low frequencies about 60 days after the burst. The 1390 MHz light curve barely evolved between 60 and 150 days, but its evolution is also marginally consistent with a F{\nu} \propto t0.8 rise seen in higher frequencies. We model the radio data and archival X-ray, optical and high-frequency radio data with models of top-hat and Gaussian structured GRB jets. We performed a Markov-Chain Monte-Carlo analysis of the structured-jet parameter space. Though highly degenerate, useful bounds on the posterior probability distributions can be obtained. Our bounds of the viewing angle ({\theta}v) are consistent with that inferred from the gravitational wave signal. We estimate the energy budget in prompt emission to be an order of magnitude lower than that in the afterglow blast-wave.

[243] arXiv:1803.03641v1 [pdf, vox]

X-ray emission from black-hole and neutron-star binaries

Tomaso M. Belloni
Submitted Friday 09 March 2018 @ 11:12:18 GMT
To appear in HIGH TIME RESOLUTION ASTROPHYSICS - XXVII Canary Islands Winter School of Astrophysics (ed. Tariq Shahbaz. Jorge Casares Vel\'azquez, Teodoro Mu\~noz Darias)

In this chapter, I present the main X-ray observational characteristics of black-hole binaries and low magnetic field neutron-star binaries, concentrating on what can be considered similarities or differences, with particular emphasis on their fast-timing behaviour.

[244] arXiv:1803.03462v1 [pdf, vox]

Solving linear equations with messenger-field and conjugate gradients techniques - an application to CMB data analysis

J. Papez, L. Grigori, R. Stompor
Submitted Friday 09 March 2018 @ 10:50:45 GMT

We discuss linear system solvers invoking a messenger-field and compare them with (preconditioned) conjugate gradients approaches. We show that the messenger-field techniques correspond to fixed point iterations of an appropriately preconditioned initial system of linear equations. We then argue that a conjugate gradient solver applied to the same preconditioned system, or equivalently a preconditioned conjugate gradient solver using the same preconditioner and applied to the original system, will in general ensure at least a comparable and typically better performance in terms of the number of iterations to convergence and time-to-solution. We illustrate our conclusions on two common examples drawn from the Cosmic Microwave Background data analysis: Wiener filtering and map-making. In addition, and contrary to the standard lore in the CMB field, we show that the performance of the preconditioned conjugate gradient solver can depend importantly on the starting vector. This observation seems of particular importance in the cases of map-making of high signal-to-noise sky maps and therefore should be of relevance for the next generation of CMB experiments.

[245] arXiv:1803.03063v2 [pdf, vox]

The Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Release Two and Three

X. Y. Dong, Xue-Bing Wu, Y. L. Ai, J. Y. Yang, Q. Yang, F. Wang, Y. X. Zhang, A. L. Lou, H. Xu, H. L. Yuan, J. N. Zhang, M. X. Wang, L. L. Wang, Y. B. Li, F. Zuo, W. Hou, Y. X. Guo, X. Kong, X. Y. Chen, Y. Wu, H. F. Yang, M. Yang
Submitted Friday 09 March 2018 @ 08:28:59 GMT
41 pages, 13 figures, 2 electronic tables available upon inquiry, accepted by AJ

This is the second installment for the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey, which includes quasars observed from September 2013 to June 2015. There are 9024 confirmed quasars in DR2 and 10911 in DR3. After cross-match with the SDSS quasar catalogs and NED, 12126 quasars are discovered independently. Among them 2225 quasars were released by SDSS DR12 QSO catalogue in 2014 after we finalised the survey candidates. 1801 sources were identified by SDSS DR14 as QSOs. The remaining 8100 quasars are considered as newly founded, and among them 6887 quasars can be given reliable emission line measurements and the estimated black hole masses. Quasars found in LAMOST are mostly located at low-to-moderate redshifts, with a mean value of 1.5. The highest redshift observed in DR2 and DR3 is 5. We applied emission line measurements to H$\alpha$, H$\beta$, Mg{\sc ii} and C{\sc iv}. We deduced the monochromatic continuum luminosities using photometry data, and estimated the virial black hole masses for the newly discovered quasars. Results are compiled into a quasar catalog, which will be available online.

[246] arXiv:1803.03411v1 [pdf, vox]

Criterions for retrograde rotation of accreting black holes

A. G. Mikhailov, M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili, S. D. Buliga
Submitted Friday 09 March 2018 @ 08:20:31 GMT
5 pages

Rotating supermassive black holes produce jets and their origin is connected to magnetic field that is generated by accreting matter flow. There is a point of view that electromagnetic fields around rotating black holes are brought to the hole by accretion. In this situation the prograde accreting disks produce weaker large-scale black hole threading magnetic fields, implying weaker jets that in retrograde regimes. The basic goal of this paper is to find the best candidates for retrograde accreting systems in observed active galactic nuclei. We show that active galactic nuclei with low Eddington ratio are really the best candidates for retrograde systems. This conclusion is obtained for kinetically dominated FRII radio galaxies, flat spectrum radio loud narrow line Seyfert I galaxies and a number of nearby galaxies. Our conclusion is that the best candidates for retrograde systems are the noticeable population of active galactic nuclei in the Universe. This result corresponds to the conclusion that in the merging process the interaction of merging black holes with a retrograde circumbinary disk is considerably more effective for shrinking the binary system.

[247] arXiv:1803.03410v1 [pdf, vox]

Spectroscopic and physical parameters of Galactic O-type stars. III. Mass discrepancy and rotational mixing

Nevena Markova, Joachim Puls, Norbert Langer
Submitted Friday 09 March 2018 @ 08:04:51 GMT
30 pages, 16 figures, 3 appendices

Massive stars play a key role in the evolution of the Universe. Our goal is to compare observed and predicted properties of single Galactic O stars to identify and constrain uncertain physical parameters and processes in stellar evolution and atmosphere models. We used a sample of 53 objects with spectral types from O3 to O9.7. For 30 of these, we determined the main photospheric and wind parameters, using optical spectroscopy and applying the FASTWIND code. For the remaining objects, literature data, obtained by means of the CMFGEN code, were used instead. The properties of our sample were compared to published predictions based on two grids evolution models that include rotationally induced mixing. Within each luminosity class, we find a close correlation of N surface abundance and luminosity, and a stronger N enrichment in more massive and evolved O stars. Additionally, a correlation of the surface nitrogen and helium abundances is observed. The large number of nitrogen-enriched stars above ~30 solar masses argues for rotationally induced mixing as the most likely explanation. However, none of the considered models can match the observed trends correctly, especially in the high mass regime. We confirm mass discrepancy for objects in the low mass O-star regime. We conclude that the rotationally induced mixing of helium to the stellar surface is too strong in some of the models. We also suggest that present inadequacies of the models to represent the N enrichment in more massive stars with relatively slow rotation might be related to problematic efficiencies of rotational mixing. We are left with a picture in which invoking binarity and magnetic fields is required to achieve a more complete agreement of the observed surface properties of a population of massive main- sequence stars with corresponding evolutionary models.

[248] arXiv:1803.03405v1 [pdf, vox]

Bridging the Gap: Capturing the Ly$α$ Counterpart of a Type-II Spicule and its Heating Evolution with VAULT2.0 and IRIS Observations

Georgios Chintzoglou, Bart De Pontieu, Juan Martínez-Sykora, Tiago M. D. Pereira, Angelos Vourlidas, Samuel Tun Beltran
Submitted Friday 09 March 2018 @ 07:43:28 GMT
15 pages, 5 figures and one online movie. Accepted for publication in the Astrophysical Journal

We present results from an observing campaign in support of the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0 is a Ly$\alpha$ (1216 \AA) spectroheliograph capable of providing spectroheliograms at high cadence. Ly$\alpha$ observations are highly complementary to the IRIS observations of the upper chromosphere and the low transition region (TR) but have previously been unavailable. The VAULT2.0 data provide new constraints on upper-chromospheric conditions for numerical models. The observing campaign was closely coordinated with the IRIS mission. Taking advantage of this simultaneous multi-wavelength coverage of target AR 12172 and by using state-of-the-art radiative-MHD simulations of spicules, we investigate in detail a type-II spicule associated with a fast (300 km s$^{-1}$) network jet recorded in the campaign observations. Our analysis suggests that spicular material exists suspended high in the atmosphere but in lower temperatures (seen in Ly$\alpha$) until it is heated and becomes visible in TR temperatures as a network jet. The heating begins lower in the spicule and propagates upwards as a rapidly propagating thermal front. The front is then observed as fast, plane-of-the-sky motion typical of a network jet, but contained inside the pre-existing spicule. This work supports that the high speeds reported in network jets should not be taken as real mass upflows but only as apparent speeds of a rapidly propagating heating front along the pre-existing spicule.

[249] arXiv:1803.03388v1 [pdf, vox]

Multi-D Simulations of Ultra-Stripped Supernovae to Shock Breakout

B. Müller, D. Gay, A. Heger, T. Tauris, S. A. Sim
Submitted Friday 09 March 2018 @ 05:43:46 GMT
15 pages, 15 figures, submitted to MNRAS

The recent discoveries of many double neutron star systems and their detection as LIGO-Virgo merger events call for a detailed understanding of their origin. Explosions of ultra-stripped stars in binary systems have been shown to play a key role in this context and have also generated interest as a potential explanation for rapidly evolving hydrogen-free transients. Here we present the first attempt to model such explosions based on binary evolution calculations that follow the mass transfer to the companion to obtain a consistent core-envelope structure as needed for reliable predictions of the supernova transient. We simulate the explosion in 2D and 3D, and confirm the modest explosion energies ~10^50erg and small kick velocities reported earlier in 2D models based on bare carbon-oxygen cores. The spin-up of the neutron star by asymmetric accretion is small in 3D with no indication of spin-kick alignment. Simulations up to shock breakout show the mixing of sizeable amounts of iron group material into the helium envelope. In view of recent ideas for a mixing-length treatment (MLT) of Rayleigh-Taylor instabilities in supernovae, we perform a detailed analysis of the mixing, which reveals evidence for buoyancy-drag balance, but otherwise does not support the MLT approximation. The mixing may have implications for the spectroscopic signatures of ultra-stripped supernovae that need to be investigated in the future. Our stellar evolution calculation also predicts presupernova mass loss due to an off-centre silicon deflagration flash, which suggests that supernovae from extremely stripped cores may show signs of interactions with circumstellar material.

[250] arXiv:1803.03385v1 [pdf, vox]

Three-dimensional MHD Simulations of Solar Prominence Oscillations in a Magnetic Flux Rope

Yu-Hao Zhou, C. Xia, R. Keppens, C. Fang, P. F. Chen
Submitted Friday 09 March 2018 @ 05:07:10 GMT
38 pages, 12 figures, accepted by ApJ

Solar prominences are subject to all kinds of perturbations during their lifetime, and frequently demonstrate oscillations. The study of prominence oscillations provides an alternative way to investigate their internal magnetic and thermal structures as the oscillation characteristics depend on their interplay with the solar corona. Prominence oscillations can be classified into longitudinal and transverse types. We perform three-dimensional ideal magnetohydrodynamic simulations of prominence oscillations along a magnetic flux rope, with the aim to compare the oscillation periods with those predicted by various simplified models and to examine the restoring force. We find that the longitudinal oscillation has a period of about 49 minutes, which is in accordance with the pendulum model where the field-ligned component of gravity serves as the restoring force. In contrast, the horizontal transverse oscillation has a period of about 10 minutes and the vertical transverse oscillation has a period of about 14 minutes, and both of them can be nicely fitted with a two-dimensional slab model. We also find that the magnetic tension force dominates most of the time in transverse oscillations, except for the first minute when magnetic pressure overwhelms.

[251] arXiv:1803.03375v1 [pdf, vox]

A systematic study of the condensation of the corona and the application for $Γ_{\rm 2-10keV}-L_{\rm bol}/L_{\rm Edd}$ correlation in luminous active galactic nuclei

Erlin Qiao, B. F. Liu
Submitted Friday 09 March 2018 @ 03:48:24 GMT
10 pages, 13 figures, Accepted for publication by MNRAS

In this paper, we explained the observed $\Gamma_{\rm 2-10keV}-L_{\rm bol}/L_{\rm Edd}$ correlation in luminous active galactic nuclei within the framework of the condensation of the corona around a supermassive black hole (Liu et al. 2015; Qiao & Liu 2017). Specifically, we systemically test the effects of black hole mass $M$, the viscosity parameter $\alpha$, and the magnetic parameter $\beta$ (with magnetic pressure $p_{\rm m}=B^2/{8\pi}=(1-\be​ta)p_{\rm tot}$, $p_{\rm tot}=p_{\rm gas}+p_{\rm m}$) on the structure of the accretion disc and the corona, as well as the corresponding emergent spectra. It is found that the hard X-ray photon index $\Gamma_{\rm 2-10keV}$ nearly does not change with changing black hole mass $M$, or changing magnetic parameter $\beta$. Meanwhile, it is found that the geometry of the accretion flow, i.e., the relative configuration of the disc and corona, as well as the emergent spectra can be strongly affected by changing the value of $\alpha$. By comparing with a sample composed of 29 luminous active galactic nuclei with well constrained X-ray spectra and Eddington ratios, it is found that the observed $\Gamma_{\rm 2-10keV}-L_{\rm bol}/L_{\rm Edd}$ correlation can be well matched with a relatively bigger value of $\alpha$, i.e., $\alpha \sim 1$, as previously also suggested by Narayan (1996) for luminous accreting black holes.

[252] arXiv:1803.03368v1 [pdf, vox]

Fundamentals of the orbit and response for TianQin

Xin-Chun Hu, Xiao-Hong Li, Yan Wang, Wen-Fan Feng, Ming-Yue Zhou, Yi-Ming Hu, Shou-Cun Hu, Jian-Wei Mei, Cheng-Gang Shao
Submitted Friday 09 March 2018 @ 03:15:42 GMT
19 pages, 4 figures, to be published in CQG

TianQin is a space-based laser interferometric gravitational wave detector aimed at detecting gravitational waves at low frequencies (0.1 mHz -- 1 Hz). It is formed by three identical drag-free spacecrafts in an equilateral triangular constellation orbiting around the Earth. The distance between each pair of spacecrafts is approximately $1.7 \times 10^{5} ~\rm{km}$. The spacecrafts are interconnected by infrared laser beams forming up to three Michelson-type interferometers. The detailed mission design and the study of science objectives for the TianQin project depend crucially on the orbit and the response of the detector. In this paper, we provide the analytic expressions for the coordinates of the orbit for each spacecraft in the heliocentric-eclipti​c coordinate system to the leading orders. This enables a sufficiently accurate study of science objectives and data analysis, and serves as a first step to further orbit design and optimization. We calculate the response of a single Michelson detector to plane gravitational waves in arbitrary waveform which is valid in the full range of the sensitive frequencies. It is then used to generate the more realistic sensitivity curve of TianQin. We apply this model on a reference white-dwarf binary as a proof of principle.

[253] arXiv:1803.03343v1 [pdf, vox]

Thermal History Of Cbb Chondrules And Cooling Rate Distributions Of Ejecta Plumes

R. H. Hewins, C. Condie, M. Morris, M. L. A. Richardson, N. Ouellette, M. Metcalf
Submitted Friday 09 March 2018 @ 01:02:14 GMT
Accepted to The Astrophysical Journal Letters

It has been proposed that some meteorites, CB and CH chondrites, contain material formed as a result of a protoplanetary collision during accretion. Their melt droplets (chondrules) and FeNi metal are proposed to have formed by evaporation and condensation in the resulting impact plume. We observe that the SO (skeletal olivine) chondrules in CBb chondrites have a blebby texture and an enrichment in refractory elements not found in normal chondrules. Since the texture requires complete melting, their maximum liquidus temperature 1928 K represents a minimum temperature for the putative plume. Dynamic crystallization experiments show that the SO texture can be created only by brief reheating episodes during crystallization giving partial dissolution of olivine. The ejecta plume formed in a smoothed particle hydrodynamics (SPH) simulation (Asphaug et al., 2011) served as the basis for 3D modeling with the adaptive mesh refinement (AMR) code FLASH4.3. Tracer particles that move with the fluid cells are used to measure the in situ cooling rates. Their cooling rates are ~10,000K/hr briefly at peak temperature and, in the densest regions of the plume, ~100 K/hr for 1400-1600 K. A small fraction of cells is seen to be heating at any one time, with heating spikes explained by compression of parcels of gas in a heterogeneous patchy plume. These temperature fluctuations are comparable to those required in crystallization experiments. For the first time, we find agreement between experiment and models that supports the plume model specifically for the formation of CBb chondrules.

[254] arXiv:1803.03340v1 [pdf, vox]

Gravitationally unstable condensations revealed by ALMA in the TUKH122 prestellar core in the Orion A cloud

Satoshi Ohashi, Patricio Sanhueza, Nami Sakai, Ryo Kandori, Minho Choi, Tomoya Hirota, Quang Nguyen Luong, Ken'ichi Tatematsu
Submitted Friday 09 March 2018 @ 00:18:52 GMT
13 pages, 14 figures, 2 tables, accepted for publication in ApJ

We have investigated the TUKH122 prestellar core in the Orion A cloud using ALMA 3 mm dust continuum, N$_2$H$^+$ ($J=1-0$), and CH$_3$OH ($J_K=2_K-1_K$) molecular line observations. Previous studies showed that TUKH122 is likely on the verge of star formation because the turbulence is almost dissipated and chemically evolved among other starless cores in the Orion A cloud. By combining ALMA 12-m and ACA data, we recover extended emission with a resolution of $\sim5"$ corresponding to 0.01 pc and identify 6 condensations with a mass range of $0.1-0.4$ $M_\odot$ and a radius of $\lesssim0.01$ pc. These condensations are gravitationally bound following a virial analysis and are embedded in the filament including the elongated core with a mass of $\sim29$ $M_\odot$ and a radial density profile of $r^{-1.6}$ derived by {\it Herschel}. The separation of these condensations is $\sim0.035$ pc, consistent with the thermal jeans length at a density of $4.4\times10^5$ cm$^{-3}$. This density is similar to the central part of the core. We also find a tendency that the N$_2$H$^+$ molecule seems to deplete at the dust peak condensation. This condensation may be beginning to collapse because the linewidth becomes broader. Therefore, the fragmentation still occurs in the prestellar core by thermal Jeans instability and multiple stars are formed within the TUKH122 prestellar core. The CH$_3$OH emission shows a large shell-like distribution and surrounds these condensations, suggesting that the CH$_3$OH molecule formed on dust grains is released into gas phase by non-thermal desorption such as photoevaporation caused by cosmic-ray induced UV radiation.

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