The detectability of GRB afterglows from GW events

Assuming GW170817 is representative of short GRBs from neutron star mergers, we determine the probability that a given neutron star merger detected by LIGO/Virgo will have an observable afterglow. Using a simulated short GRB energy distribution (Lazzati et al. 2017a) and the TRAC afterglow code, we first find best-fit parameters to observations of GW170817, including VLBA position measurements. We then take this afterglow and model its X-ray, optical, and radio light curve at different observer angles, ISM densities, and distances. With this information, we determine the fraction of LIGO/Virgo neutron star merger that produce an afterglow bright enough to be observable, as a function of GW detector sensitivity. We also determine the time window over which an afterglow may be bright enough to be detected, as a function of gravitational wave strain.