Binary neutron star merger rate via the luminosity function of short gamma-ray bursts

TL;DR

This paper models the luminosity function of short gamma-ray bursts to estimate the binary neutron star merger rate and predicts gravitational wave detection rates for current and future observatories.

Contribution

It introduces a new method to derive BNSM rates from short GRB luminosity functions using pseudo-redshifts and jet angles, providing updated merger rate estimates.

Findings

Powerlaw luminosity function is ruled out by data.

Derived BNSM rate lower limits: 1.87 per year (aLIGO-Virgo), 3.11 per year (aLIGO-Virgo-KAGRA-LIGO/India).

BNSM rates from GRBs are mildly in tension with direct BNS observations.

Abstract

The luminosity function of short Gamma Ray Bursts (GRBs) is modelled by using the available catalogue data of all short GRBs (sGRBs) detected till October, 2017. The luminosities are estimated via the `pseudo-redshifts' obtained from the `Yonetoku correlation', assuming a standard delay distribution between the cosmic star formation rate and the production rate of their progenitors. While the simple powerlaw is ruled out to high confidence, the data is fit well both by exponential cutoff powerlaw and broken powerlaw models. Using the derived parameters of these models along with conservative values in the jet opening angles seen from afterglow observations, the true rate of short GRBs are derived. Assuming a short GRB is produced from each binary neutron star merger (BNSM), the rate of gravitational wave (GW) detections from these mergers are derived for the past, present and future configurations of the GW detector networks. Stringent lower limits of $1.87 \pyr$ for the aLIGO-VIRGO, and $3.11 \pyr$ for the upcoming aLIGO-VIRGO-KAGRA-LIGO/India configurations are thus derived for the BNSM rate at $68 \%$ confidence. The BNSM rates calculated from this work and that independently inferred from the observation of the only confirmed BNSM observed till date, are shown to have a mild tension; however the scenario that all BNSMs produce sGRBs cannot be ruled out.