2019ApJ...877L..39C

Multimessenger observations of the binary neutron star merger GW170817 have enabled the discovery of a diverse array of electromagnetic counterparts to compact binary mergers, including an unambiguous kilonova, a short gamma-ray burst, and a late-time radio jet. Beyond these counterparts, compact binary mergers are additionally predicted to be accompanied by prompt low-frequency radio emission. The successful observation of a prompt radio counterpart would be immensely valuable, but is made difficult by the short delay between the gravitational-wave and prompt electromagnetic signals, as well as by the poor localization of gravitational-wave sources. Here, we present the first search for prompt radio emission accompanying a gravitational-wave event, targeting the binary black hole merger GW170104 detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo during their second (O2) observing run. Using the Owens Valley Radio Observatory Long Wavelength Array, we search a ∼900 deg² region for transient radio emission within approximately one hour of GW170104, obtaining an upper limit of 2.5 x 10⁴¹ erg s^–1 on its equivalent isotropic luminosity between 27 and 84 MHz. We additionally discuss plans to target binary neutron star mergers in Advanced LIGO and Virgo's upcoming O3 observing run.