Gamma-ray burst models in light of the GRB 170817A - GW170817 connection

TL;DR

This paper analyzes gamma-ray burst models in light of the first confirmed association with a gravitational wave event, finding internal shocks and external shock models most consistent with observations, while challenging photospheric models.

Contribution

It provides a comparative analysis of different GRB emission models based on the GW170817/GRB 170817A event, highlighting the most plausible mechanisms.

Findings

Internal shocks best explain the observed peak energy and total energy.

External shock models can reproduce the GRB pulse with consistent parameters.

Photospheric models face difficulties accounting for the observations.

Abstract

For the first time, a short gamma-ray burst (GRB) was unambiguously associated with a gravitational wave (GW) observation from a binary neutron star (NS) merger. This allows us to link the details of the central engine properties to GRB emission models. We find that photospheric models (both dissipative and non-dissipative variants) have difficulties accounting for the observations. Internal shocks give the most natural account of the observed peak energy, viewing angle and total energy. We also show that a simple external shock model can reproduce the observed GRB pulse with parameters consistent with those derived from the afterglow modeling. We find a simple cocoon shock breakout model is in mild tension with the observed spectral evolution, however it cannot be excluded based on gamma-ray data alone. Future joint observations of brighter GRBs will pose even tighter constraints on prompt emission models.