The short-duration GRB 050724 host galaxy in the context of the long-duration GRB hosts

We report optical and near-infrared broad band observations of the short-duration GRB 050724 host galaxy, used to construct its spectral energy distribution (SED). Unlike the hosts of long-duration gamma-ray bursts (GRBs), which show younger stellar population, the SED of the GRB 050724 host galaxy is optimally fitted with a synthetic elliptical galaxy template based on an evolved stellar population (age ~2.6 Gyr). The SED of the host is difficult to reproduce with non-evolving metallicity templates. In contrast, if the host galaxy metallicity enrichment is considered, the synthetic templates fit satisfactorily the observed SED. The internal host extinction is low (Av ~< 0.4 mag) so it cannot explain the faintness of the afterglow. The host galaxy is more massive (5x10^10 Msun) and luminous (~1.1 L*) than most of the long-duration GRB hosts. A statistical comparison based on ages of short- and long-duration GRB host galaxies strongly suggests that short-duration GRB hosts contain, on average, older progenitors. These findings support a different origin for short- and long-duration GRBs