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

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.