Linking Short Gamma Ray Bursts and their Host Galaxies

The luminosities of short gamma ray burst host galaxies are anticorrelated with both the isotropic equivalent gamma ray energy and the gamma ray luminosity of the explosions. Observational selection effects only strengthen the significance of this correlation. The correlation may indicate that there are two physically distinct groups of SGRBs. If so, it requires that the more luminous class of explosions be associated with the younger class of progenitors. Alternatively, it could be due to a continuous distribution of burst and host properties. As one possible explanation, we find that the effect of binary neutron star masses on inspiral time and energy reservoir produces a correlation of the appropriate sign, but does not automatically reproduce the correlation slope or the full range of SGRB energy scales. Any future model of SGRB progenitors needs to reproduce this correlation.