GW170817: implications for the local kilonova rate and for surveys from ground-based facilities

Abstract

We compute the local rate of events similar to GRB 170817A, which has been recently found to be associated with a kilonova (KN) outburst. Our analysis finds an observed rate of such events of R${}_{KN}\sim 352_{-281}^{+810}$ Gpc${}^{-3}$yr${}^{-1}$. After comparing at their face values this density of sGRB outbursts with the much higher density of Binary Neutron Star (BNS) mergers of 1540${}_{-1220}^{+3200}$ Gpc${}^{-3}$yr${}^{-1}$, estimated by LIGO-Virgo collaboration, one can conclude, admittedly with large uncertainty that either only a minor fraction of BNS mergers produces sGRB/KN events or the sGRBs associated with BNS mergers are beamed and observable under viewing angles as large as $\theta$ $\le$ $40^{\circ }$. Finally we provide preliminary estimates of the number of sGRB/KN events detected by future surveys carried out with present/future ground-based/space facilities, such as LSST, VST, ZTF, SKA and THESEUS.

MNRAS accepted, 6 pages, 1 figure