Radio afterglows of binary neutron star mergers: a population study for current and future gravitational wave observing runs

R Duque,F Daigne,R Mochkovitch

doi:10.1051/0004-6361/201935926

Abstract

Following the historical observations of GW170817 and its multi-wavelength afterglow, more radio afterglows from neutron star mergers are expected in the future as counterparts to gravitational wave inspiral signals. Our aim is to describe these events using our current knowledge of the population of neutron star mergers based on gamma-ray burst science, and taking into account the sensitivities of current and future gravitational wave and radio detectors. We combined analytical models for the merger gravitational wave and radio afterglow signals to a population model prescribing the energetics, circum-merger density and other relevant parameters of the mergers. We reported the expected distributions of observables (distance, orientation, afterglow peak time and flux, etc.) for future events and studied how these can be used to further probe the population of binary neutron stars, their mergers and related outflows during future observing campaigns. In the case of the O3 run of the LIGO-Virgo Collaboration, the radio afterglow of one third of gravitational-wave-detected mergers should be detectable (and detected if the source is localized thanks to the kilonova counterpart) by the Very Large Array. Furthermore, these events should have viewing angles similar to that of GW170817. These findings confirm the radio afterglow as a powerful insight into these events, although some key afterglow-related techniques, such as very long baseline interferometry imaging of the merger remnant, may no longer be feasible as the gravitational wave horizon increases.

Highlights

The first detection of the gravitational waves (GW) from the inspiral phase of a binary neutron star merger (Abbott et al 2017, 2019) was followed by all three electromagnetic counterparts expected after the coalescence: a short gamma-ray burst (GRB; Goldstein et al 2017; Savchenko et al 2017) and its multi-wavelength afterglow (AG) in the X-ray (Haggard et al 2017; Margutti et al 2017; Troja et al 2017; D’Avanzo et al 2018), radio (Hallinan et al 2017) and optical bands (Lyman et al 2018), and an optical-IR thermal transient source (Evans et al 2017; Valenti et al 2017; Coulter et al 2018)
In the context of the present O3 and future observing runs of the LIGO-Virgo Collaboration (LVC), we would like to know what to expect regarding the afterglows of future binary neutron star (BNS) mergers: the rates of GW and joint GW-AG events; the distributions of event observables, such as distance D, viewing angle θv, radio afterglow time of peak tp and peak flux Fp, and remnant proper motion μ; and the sensitivity of these to the population’s characteristics and to the multi-messenger detector configuration
We studied the population of binary neutron star mergers to be observed jointly through GW and their radio afterglows in future multi-messenger observing campaigns

Summary

Introduction

The first detection of the gravitational waves (GW) from the inspiral phase of a binary neutron star merger (Abbott et al 2017, 2019) was followed by all three electromagnetic counterparts expected after the coalescence: a short gamma-ray burst (GRB; Goldstein et al 2017; Savchenko et al 2017) and its multi-wavelength afterglow (AG) in the X-ray (Haggard et al 2017; Margutti et al 2017; Troja et al 2017; D’Avanzo et al 2018), radio (Hallinan et al 2017) and optical bands (Lyman et al 2018), and an optical-IR thermal transient source (Evans et al 2017; Valenti et al 2017; Coulter et al 2018) The latter transient allowed for the localization of the event with sub-arcsecond precision in the S0-type galaxy NGC 4993 at a distance of 40.7 ± 3.3 Mpc (Palmese et al 2017; Cantiello et al 2018). In the context of the present O3 and future observing runs of the LIGO-Virgo Collaboration (LVC), we would like to know what to expect regarding the afterglows of future binary neutron star (BNS) mergers: the rates of GW and joint GW-AG events; the distributions of event observables, such as distance D, viewing angle θv, radio afterglow time of peak tp and peak flux Fp, and remnant proper motion μ; and the sensitivity of these to the population’s characteristics and to the multi-messenger detector configuration

Objectives

Methods

Findings

Conclusion