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  • Electromagetic Counterparts of Gravitational Wave Sources

    Prof Iain Steele & Dr Chris Copperwheat

    Figure 1: An ariel view of the LIGO Livingston Observatory (LLO) in Louisiana. Image taken from the LIGO website.
    Figure 2: The Liverpool Telescope (LT), a 2-metre fully robotic telescope based on the Canary island of La Palma, which is owned and operated by LJMU with support from STFC. The LT is one of the world's leading facilities for time domain astronomy.

    Background information

    In 2015 the first direct detection of gravitational waves (GW) was made with the Advanced LIGO detector - surely one of the most exciting discoveries in physics that we will see in our lifetimes. The source of the signal in both cases was the merger of a binary pair of black holes. The next milestone is the detection of 'electromagnetically bright' events: GW events for which there is a counterpart we can observe with our telescopes. This is important for two reasons: the counterpart provides an independent verification of any event, and measurement of the electromagnetic emission is necessary for the scientific classification and exploitation of the object in question. Merging pairs of neutron stars are EM bright: we believe such events are the cause of short gamma-ray bursts. Neutron star events produce a weaker GW signal than black hole events but are much more common, so as the sensitivity of the GW detectors increases they should begin to dominate the population of detected sources. Other possible gravitational wave detections include `bursts' from other explosive events, such as supernovae. We are at the beginning of a whole new type of astronomy in which exotic phenomena can be detected for the first time by non-electromagnetic means, providing new windows on the time variable universe.

    Research project

    As one of ~50 astronomical groups worldwide which have joined the gravitational wave follow-up programme, LJMU ARI plans to be at the forefront of this new era. However, there are some significant astronomical challenges. The electromagnetic signature of a GW counterpart is somewhat uncertain at this stage. Additionally, the gravitational wave detectors will provide limited positional information on any detection, so astronomical follow-up will need to survey a huge area of sky. At ARI we enjoy a significant advantage in the form of the 2-metre Liverpool Telescope (LT): a fully robotic facility based on one of the world's best observing sites. One of the main problems is that the positional uncertainty is such that there will be many other time variable `transients' in the same region: variable stars, dwarf novae, unrelated supernovae etc. Distinguishing the true GW counterpart from these unrelated (but still potentially scientifically interesting) objects will be challenging, and will require the creation and deployment of classification algorithms which will allow the robotic LT to rapidly and automatically choose which transients to pursue. The problem of automatic classification is an increasingly recognised one in modern time domain astrophysics, and the development of such software tools will also be vital for the next generation of supernova surveys, such as LSST: another project in which we hope to play a prominent role. The exploitation of GW counterparts is also a key science goal for Liverpool Telescope 2: the planned 4-metre successor to the existing telescope, which will begin operations in the next decade. The lessons we learn in these early years of GW science will potentially have a considerable influence on the design of that new facility.

    The student will work with the members of both the Liverpool Telescope and Time Domain Astrophysics groups on the problems of detection and exploitation of gravitational wave counterparts using the LT. This is an observational astronomy project which will involve working with both new and archival LT data, and potentially data from other facilities. We anticipate the development of classification algorithms will be an important part of the project, so experience with programming is desirable but not essential.