GRB 170817A as a jet counterpart to gravitational wave trigger GW 170817

TL;DR

This paper models the afterglow emission of GRB 170817A, associated with GW 170817, exploring various jet configurations to understand the observed afterglow and inform future gravitational wave counterpart studies.

Contribution

The study presents detailed modeling of the afterglow for different jet structures and viewing angles, advancing understanding of jet emission mechanisms in neutron star mergers.

Findings

Late-time afterglow fits a structured jet viewed at moderate inclination

All jet models predict observable afterglows on various timescales

The models can be applied to future GW-detected neutron star merger counterparts

Abstract

{\it Fermi}/GBM (Gamma-ray Burst Monitor) and INTEGRAL (the International Gamma-ray Astrophysics Laboratory) reported the detection of the $\gamma$-ray counterpart, GRB 170817A, to the LIGO (Light Interferometer Gravitational-wave Observatory)/{\it Virgo} gravitational wave detected binary neutron star merger, GW 170817. GRB 170817A is likely to have an internal jet or another origin such as cocoon emission, shock-breakout, or a flare from a viscous disc. In this paper, we assume that the $\gamma$-ray emission is caused by energy dissipation within a relativistic jet and we model the afterglow synchrotron emission from a reverse- and forward-shock in the outflow. We show the afterglow for a low-luminosity $\gamma$-ray burst (GRB) jet with a high Lorentz-factor ($\Gamma$); a low-$\Gamma$ and low-kinetic energy jet; a low-$\Gamma$, high kinetic energy jet; structured jets viewed at an inclination within the jet-half-opening angle; and an off-axis `typical' GRB jet. All jet models will produce observable afterglows on various timescales. The late-time afterglow from 10-110 days can be fit by a Gaussian structured jet viewed at a moderate inclination, however, the GRB is not directly reproduced by this model. These jet afterglow models can be used for future GW detected NS merger counterparts with a jet afterglow origin.