Gamma-Ray Bursts from Neutron Star Mergers and Evolution of Galaxies

Abstract

Most of proposed models of cosmological gamma-ray bursts (GRBs) are associated to gravitational collapses of massive stars, and hence evolution of the GRB rate, which is crucially important in GRB intensity distribution analysis, is determined by the cosmic star formation history. Here we present complementary results of GRB logN-logP analysis, which were omitted in the previous paper (Totani 1997, ApJ, 486, L71). A unique feature of the binary neutron-star merger scenario, in contrast to other scenarios associated to single stellar collapses, is that a time delay during binary spiral-in phase emitting gravitational waves is not negligible and makes the rate evolution flatter than that of star formation rate. We show that binary merger scenario is more favored than single stellar collapses. The estimated peak luminosity and total emitted energy in rest-frame 50-300 keV range is 1--3 $\times 10^{51} (Ω/ 4 π)$ erg/s and 1--3 $\times 10^{52} (Ω/ 4 π)$ erg, respectively, where $Ω$ is opening angle of gamma-ray emission. Absolute rate comparison between GRBs and neutron-star mergers suggests that a beaming factor of $(Ω/4π)^{-1} \sim$ a few hundreds is required. High-$z$ SFR data ($z>2$) based on UV luminosity need to be corrected upwards by a factor of 5--10 for a good fit, and this is likely explained by the dust extinction effect.