Constraining short gamma-ray burst jet properties with gravitational waves and gamma rays

TL;DR

This paper introduces a Bayesian method to determine the geometry of short gamma-ray burst jets using combined gravitational-wave and gamma-ray observations, enabling better understanding of jet properties and their distributions.

Contribution

It presents a novel Bayesian approach for constraining short GRB jet properties with multi-messenger data, improving measurements of jet angles and energies.

Findings

For 100 detections, can constrain average jet opening angle within 10 degrees.

The method distinguishes different angular emission profiles based on energy distribution constraints.

Multi-messenger observations significantly improve understanding of GRB jet geometries.

Abstract

Gamma-ray burst (GRB) prompt emission is highly beamed, and understanding the jet geometry and beaming configuration can provide information on the poorly understood central engine and circum-burst environment. Prior to the advent of gravitational-wave astronomy, astronomers relied on observations of jet breaks in the multi-wavelength afterglow to determine the GRB opening angle, since the observer's viewing angle relative to the system cannot be determined from the electromagnetic data alone. Gravitational-wave observations, however, provide an independent measurement of the viewing angle. We describe a Bayesian method for determining the geometry of short GRBs using coincident electromagnetic and gravitational-wave observations. We demonstrate how an ensemble of multi-messenger detections can be used to measure the distributions of the jet energy, opening angle, Lorentz factor, and angular profile of short GRBs; we find that for a population of 100 such observations, we can constrain the mean of the opening angle distribution to within 10 degrees regardless of the angular emission profile. Conversely, the constraint on the energy distribution depends on the shape of the profile, which can be distinguished.