Radio Counterparts of Compact Binary Mergers detectable in Gravitational Waves: A Simulation for an Optimized Survey

TL;DR

This study models and optimizes radio follow-up surveys for detecting electromagnetic counterparts of gravitational wave mergers, focusing on synchrotron emissions from merger ejecta and jets, to enhance detection prospects with current and future radio telescopes.

Contribution

It provides a detailed simulation of radio signals from GW mergers and proposes an optimized multi-epoch survey strategy at 1.4 GHz to maximize detection of radio counterparts.

Findings

Detectable distances up to 1 Gpc for GW events.

20-60% of long-lasting radio remnants are detectable under certain conditions.

5-20% of orphan radio afterglows are detectable with specific kinetic energies.

Abstract

Mergers of binary neutron stars and black hole-neutron star binaries produce gravitational-wave (GW) emission and outflows with significant kinetic energies. These outflows result in radio emissions through synchrotron radiation. We explore the detectability of these synchrotron generated radio signals by follow-up observations of GW merger events lacking a detection of electromagnetic counterparts in other wavelengths. We model radio light curves arising from (i) sub-relativistic merger ejecta and (ii) ultra-relativistic jets. The former produces radio remnants on timescales of a few years and the latter produces $\gamma$-ray bursts in the direction of the jet and orphan-radio afterglows extending over wider angles on timescales of weeks. Based on the derived light curves, we suggest an optimized survey at $1.4$ GHz with five epochs separated by a logarithmic time interval. We estimate the detectability of the radio counterparts of simulated GW-merger events to be detected by advanced LIGO and Virgo by current and future radio facilities. The detectable distances for these GW merger events could be as high as 1 Gpc. $20$--$60\%$ of the long-lasting radio remnants will be detectable in the case of the moderate kinetic energy of $3\cdot 10^{50}$ erg and a circum-merger density of $0.1 {\rm cm^{-3}}$ or larger, while $5$--$20\%$ of the orphan radio afterglows with kinetic energy of $10^{48}$ erg will be detectable. The detection likelihood increases if one focuses on the well-localizable GW events. We discuss the background noise due to radio fluxes of host galaxies and false positives arising from extragalactic radio transients and variable Active Galactic Nuclei and we show that the quiet radio transient sky is of great advantage when searching for the radio counterparts.