The Redshift and the Host Galaxy of GRB 980613: A Gamma-Ray Burst from a Merger-induced Starburst?


We present the optical and near-IR identification and spectroscopy of the host galaxy of gamma-ray burst GRB 980613. The burst was apparently associated with the optically (rest-frame UV) brightest component of an apparent system of at least five galaxies or galaxy fragments, at least two of which are at a redshift of z=1.0969. The component we identify as the host galaxy shows a moderately high unobscured star formation rate, SFRåisebox-0.5ex 5 M$_solar $ yr$^-1$, but a high SFR per unit mass, indicative of a starburst. The image components show a broad range of (R-K) colors, with two of them being very red, possibly due to dust. The overall morphology of the system can be naturally interpreted as a strong tidal interaction of two or more galaxies, at a redshift where such events were much more common than now. Given the well- established causal link between galaxy mergers and starbursts, we propose that this is a strong case for a GRB originating from a merger-induced starburst system. This supports the proposed link between GRBs and massive star formation.

Partially based on the observations obtained at the W. M. Keck Observatory, which is operated by the California Association for Research in Astronomy, a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

Astrophysical Journal Letters