2018MNRAS.481.4355D

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_∼352⁺⁸¹⁰_–281 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⁺³²⁰⁰_–1220 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 short gamma-ray bursts (sGRB)/KN events or the sGRBs associated with BNS mergers are beamed and observable under viewing angles as large as θ <= 40°. 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.