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

¹ Instituto de Astrofísica de Andalucía (IAA – CSIC), Apartado de Correos, 3.004, 18.080 Granada, Spain e-mail: jgu@iaa.es
² INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone (Rome), Italy
³ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁴ International School for Advanced Studies (SISSA – ISAS), via Beirut 2-4, 34014 Trieste, Italy
⁵ INAF – Osservatorio Astronomico di Padova, via dell'Osservatorio 8, 36012 Asiago (VI), Italy
⁶ Astronomical Observatory of Nikolaev State University, Nikolskaja, 24, Nikolaev, 54030, Ukraine
⁷ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark

Received: 18 October 2005
Accepted: 13 December 2005

Abstract

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 populations, 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 short GRB host galaxy metallicity enrichment is considered, the synthetic templates fit the observed SED satisfactorily. The internal host extinction is low ( mag) so it cannot explain the faintness of the afterglow. This short GRB host galaxy is more massive () and luminous () than most of the long-duration GRB hosts. A statistical comparison based on the 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.