Short gamma-ray bursts as a possible probe of binary neutron star mergers

Abstract

We study the properties of short gamma-ray bursts (GRBs), based on the assumption that they are all connected to the binary neutron star mergers, whose formation mechanism contains a large amount of uncertainty. In particular, the merger time distribution is focused on, which is essential for short GRB rate estimate; we simply parameterize it as P_m(t)\propto t^αwith lower cutoff time-scale τ. The short GRB rate, calculated using such a parameterization with a specific model of cosmic star formation rate, is found to be quite insensitive to the value of τ, but considerably sensitive to α. With such formation rate models, the peak flux distribution observed by BATSE is fitted. In the fitting process, the local short GRB rate ρ_0 is treated as one of free parameters, giving the best fit when ρ_0 = 0.1--2 yr^{-1} Gpc^{-3}, depending on the other free parameters as well as the formation rate model represented by (τ,α). We also discuss several implications for the intrinsic properties of possible sources of short GRBs, such as jet structure, intrinsic luminosity function, and intrinsic duration distribution.