|
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.
|
