# A First Search for Prompt Radio Emission from a Gravitational-Wave Event

## TL;DR

This paper reports the first search for prompt low-frequency radio emission from a gravitational-wave event, specifically GW170104, setting upper limits and discussing future observations of neutron star mergers.

## Contribution

It introduces the first search for prompt radio signals from a gravitational-wave event, expanding multimessenger astronomy to include low-frequency radio observations.

## Key findings

- No prompt radio emission detected from GW170104.
- Established an upper limit of 2.5×10^41 erg/s on radio luminosity.
- Discussed future plans for neutron star merger radio searches.

## Abstract

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 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 LIGO and Virgo gravitational-wave observatories during their second (O2) observing run. Using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), we search a $\sim900\,\mathrm{deg}^2$ region for transient radio emission within approximately one hour of GW170104, obtaining an upper limit of $2.5\times10^{41}\,\mathrm{erg}\,\mathrm{s}^{-1}$ on its equivalent isotropic luminosity between 27-84 MHz. We additionally discuss plans to target binary neutron star mergers in Advanced LIGO and Virgo's upcoming O3 observing run.