Estimating the true energy and rate of short-duration GRBs

The detection of jetbreaks in short GRBs afterglow light curves providedevidence that their emission is collimated. The knowledge of the jet openingangle (theta_j) distribution of short GRBs is mandatory for a properunderstanding of the true energetics and rate of this class of events. Only ahandful of the short GRBs observed by Swift to date has a robust estimate oftheta_j. We propose here to overcome this limit by carrying out ToO XMMNewtonobservations of a subsample of Swift short GRBs (selected maximizing thepossibility of multiwavelength followup), hunting for a jetbreak signature intheir latetime Xray afterglow light curves. The increasing evidence forcompact object binary progenitors makes short GRBs one of the most promising sources of GWs. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]