Probing Binary Neutron Star Merger Ejecta and Remnants with Gravitational Wave and Radio Observations

TL;DR

This study assesses the detectability of radio signals from binary neutron star mergers using gravitational wave and radio observations, emphasizing future detector capabilities and their potential to observe afterglows and remnants.

Contribution

It provides a comprehensive analysis of how next-generation gravitational wave and radio telescopes can improve detection rates and localization of BNS merger counterparts.

Findings

Next-generation GW detectors will significantly increase well-localized BNS detections.

Future radio arrays can detect short GRB-like afterglows for many BNS mergers.

Current radio arrays can detect some signals but are limited by synchrotron self-absorption.

Abstract

We present a study aimed at quantifying the detectability of radio counterparts of binary neutron star (BNS) mergers with total masses $\lesssim 3$\,M$_{\odot}$, which may form neutron star (NS) remnants. We focus on mergers localized by gravitational-wave (GW) observations to sky areas $\lesssim 10$\,deg$^2$, a precision that greatly facilitates optical counterpart identification and enables radio discovery even without detections at other wavelengths. Widely separated GW detectors are essential for building samples of well-localized BNS mergers accessible to US-based radio telescopes, with minimum yearly detection rates (assuming the smallest values of the BNS local merger rate) ranging from a few with current GW detectors to hundreds with next-generation GW instruments. Current GW networks limit well-localized detections to $z\lesssim 0.2$, while next-generation GW detectors extend the reach to $z\lesssim 0.8$, encompassing the median redshift of short gamma-ray bursts (GRBs). With next-generation radio arrays operating at a several tens of GHz and providing an order of magnitude improvement in sensitivity compared to the most sensitive ones available today, short GRB-like jet afterglows can be detected for a large fraction of the considered BNS mergers. At lower radio frequencies, detections with current radio interferometric arrays are feasible, though subject to synchrotron self-absorption effects. The enhanced sensitivity and survey speed of future radio interferometers operating at a few GHz, combined with the higher detection rate of well-localized BNSs enabled by next-generation GW observatories, are key to probing disk-wind and dynamical ejecta afterglows, as well as remnant diversity.