GRB 170817A as a jet counterpart to gravitational wave triggerGW 170817

TLDR

The γ‑ray burst GRB 170817A was detected by Fermi/GBM and INTEGRAL as the electromagnetic counterpart to the binary neutron‑star merger GW 170817, and jet models predict observable afterglows over a range of timescales. The study aims to test whether the γ‑ray emission of GRB 170817A originates from a relativistic jet by modeling its afterglow synchrotron emission from reverse and forward shocks. The authors model the afterglow synchrotron emission from reverse and forward shocks for several jet configurations—including low‑luminosity, low‑Γ, low‑kinetic‑energy, structured, and off‑axis jets—to compare with observations. The late‑time afterglow (10–110 d) is best fit by a Gaussian structured jet seen at a moderate inclination, but this model does not reproduce the prompt GRB emission.

Abstract

Fermi/GBM (Gamma-ray Burst Monitor) and INTEGRAL (the International Gamma-ray Astrophysics Laboratory) reported the detection of the γ-ray counterpart, GRB 170817A, to the LIGO (Light Interferometer Gravitational-wave Observatory)/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 γ-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 γ-ray burst (GRB) jet with a high Lorentz factor (Γ); a low-Γ and low-kinetic-energy jet; a low-Γ, 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 time-scales. The late-time afterglow from 10 to 110 d can be fitted 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 gravitational wave detected neutron star merger counterparts with a jet afterglow origin.