Radio observations of GW170817 revealed a radio afterglow that, alongside gamma-ray and x-ray emission, was produced by a mildly relativistic wide-angle outflow, created by a cocoon of emission formed during the interaction of a highly relativistic jet with surrounding material ejected during the merger. This radio afterglow is powered by synchrotron emission, which evolves on time scales of weeks to years.

However, there are many theories that predict another kind of radio signature from compact object mergers. A very bright, coherent millisecond-duration pulse of low-frequency radio emission may accompany, or even precede, the gravitational wave signal detectable by observatories like LIGO and Virgo. Such emission would provide a very powerful independent confirmation, or even advance prediction, of gravitational-wave (GW) events, as well as offering greatly improved localization.

The OVRO-LWA is a uniquely powerful follow-up facility for such GW events. The nearly full-hemisphere field of view can instantaneously cover the entire 90% confidence localization region released by LIGO and Virgo approximately 50% of the time. OVRO-LWA observes continuously, with observations saved to a 24-hour long buffer, enabling contemporaneous coverage of a GW event and making possible the detection of any precursor radio emission.

The most powerful, and technically challenging, strategy employed by OVRO-LWA to search for coherent, short-duration radio emission accompanying GW events is the buffering and coherent dedispersion of the raw voltage streams from all 352 antennas. The raw antenna voltages are stored in a large memory buffer for up to 10 minutes – within the predicted latency of LIGO/Virgo automated GW alerts. This raw voltage stream provides the high time-resolution needed to more sensitively search for the millisecond-duration pulse of the precursor radio emission.