Short GRBs: Rates and luminosity function implications: Rates and luminosity function implications

We compare the luminosity function and rate inferred from the BATSE Short Hard Bursts (SHBs) peak flux distribution with the redshift and luminosity distributions of SHBs observed by Swift/HETE-2. The Swift/HETE-2 SHB sample is incompatible with a SHB population that follows the star formation rate. However, it is compatible with a distribution of delay times after the SFR. This would be the case if SHBs are associated with the mergers of Double Neutron Star (DNS) systems. DNS may be "primordial" or can form dynamically by binary exchange interaction in globular clusters during core collapse. The implied SHB rates that we find range from ∼8 to ∼30h₇₀ ³ Gpc^-3y^-1. This rate is much higher than what was previously estimated and, when beaming is taken into account, it is comparable to the rate of neutron star mergers estimated from statistics of binary pulsars. If short GRBs are produced in mergers the implied rate practically guarantees detection by LIGO II and possibly even by LIGO I.