The potential role of binary neutron star merger afterglows in multimessenger cosmology

S Mastrogiovanni,R Duque,F Daigne,E Chassande-Mottin,R Mochkovitch

doi:10.1051/0004-6361/202040229

Abstract

Binary neutron star mergers offer a new and independent means of measuring the Hubble constant H0 by combining the gravitational-wave inferred source luminosity distance with its redshift obtained from electromagnetic follow-up. This method is limited by the intrinsic degeneracy between the system distance and orbital inclination in the gravitational-wave signal. Observing the afterglow counterpart to a merger can further constrain the inclination angle, allowing this degeneracy to be partially lifted and improving the measurement of H0. In the case of the binary neutron star merger GW170817, afterglow light-curve and imaging modeling thus allowed the H0 measurement to be improved by a factor of three. However, systematic access to afterglow data is far from guaranteed. In fact, though each one allows a leap in H0 precision, these afterglow counterparts should prove rare in forthcoming multimessenger campaigns. We combine models for emission and detection of gravitational-wave and electromagnetic radiation from binary neutron star mergers with realistic population models and estimates for afterglow inclination angle constraints. Using these models, we quantify how fast H0 will be narrowed down by successive multimessenger events with and without the afterglow. We find that because of its rareness and though it greatly refines angle estimates, the afterglow counterpart should not significantly contribute to the measurement of H0 in the long run.

Highlights

The detection of gravitational waves (GWs) from compact binary coalescence (Abbott et al 2019) has opened a new window to study the Universe
The first GW measurement of H0 was made possible by the multimessenger observation of the binary neutron star (BNS) merger GW170817 (Abbott et al 2017a) and its associated kilonova, which enabled the identification of the host galaxy and its redshift, leading to a new and independent measurement of H0 = 70+−182 km s−1 Mpc−1 (Abbott et al 2017b)
We studied the prospects of measuring the Hubble constant with GW standard sirens coupled to inclination angle measurements from merger afterglow counterparts

Summary

Introduction

The detection of gravitational waves (GWs) from compact binary coalescence (Abbott et al 2019) has opened a new window to study the Universe. If supplied with the source redshift information, GW detections can be used to measure cosmological parameters (Holz & Hughes 2005; Nissanke et al 2013; Chen et al 2018; Mortlock et al 2019), such as the Hubble constant H0. This possibility is of great interest given the current tension between the H0 measurement at early and late epochs of the Universe (Freedman 2017). In the absence of an electromagnetic counterpart, one can use the redshifts of all cataloged galaxies with positions consistent with the 3D GW skymap to measure H0 (the so-called “dark siren” method; Fishbach et al 2019; Soares-Santos et al 2019; Gray et al 2020), leverage tidal effects in the GW waveform to estimate the source redshift (Messenger & Read 2012; Del Pozzo et al 2017), or exploit the power spectrum of GWs and galaxy distributions (Mukherjee et al 2021b, 2020)

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Discussion

Conclusion