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

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 _-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 short gammaray 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.