GW170817: 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 similar to 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 gamma-ray bursts (sGRB)/KN events or the sGRBs associated with BNS mergers are beamed and observable under viewing angles as large as theta less than or similar to 40 degrees. 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.