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18th of May 2022
ATNF Colloquium
LOFAR observations of neutron star mergers
Kelly Gourdji (Swinburne University of Technology)
Abstract: Both coherent and incoherent low-frequency radio emission are predicted at various timescales when neutron stars coalesce. In this talk, I show how the Low-Frequency Array (LOFAR) is being used to catch both fast and slow radio transients related to neutron star mergers. At the earliest timescales, coherent emission resembling FRBs is predicted by several theoretical models. Testing these models can shed light on the nature of the merger remnant and other important questions, but requires rapid triggered observations. Here, I show how we are using LOFAR to trigger on short gamma-ray bursts (SGRBs) detected by Swift, which have neutron star merger progenitors. In addition to possible prompt emission, there will be a long-lasting synchrotron afterglow caused by the merger ejecta’s interaction with the ambient medium. The afterglow contains a wealth of information including the geometry and energy of the merger outflow. The biggest challenge associated with detecting the electromagnetic counterpart of gravitational wave (GW) merger events, however, is the large uncertainty (tens-hundreds of square degrees) on their locations. Here, I demonstrate our strategy which applies LOFAR’s high sensitivity and large field of view to search for GW merger radio counterparts. I present results from LOFAR follow-up observations of merger events from the last GW observing run. I also show how the high sensitivity, large field of view and range of epochs permit us to probe previously unexplored parts of general radio transient phase space. The image above shows the location probability density map of a black-hole neutron star merger detected in third gravitational wave observing run. The inset shows a green box representing coverage of the LOFAR radio map of this event. The radio map obtained covers ~21 deg^2 and has a median rms of 230 μJy.

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