Spectroscopy of the Host Galaxy of the Gamma-Ray Burst 980703

Abstract

We present spectroscopic observations of the host galaxy of GRB 980703. Several emission and absorption features are detected, making the redshift (z=0.966) completely unambiguous. This is only the third known redshift for a γ-ray burst (GRB) host. The implied isotropic γ-ray energy release from the burst is in excess of 10${}^{5}3$ ergs for a reasonable choice of cosmological parameters. The spectroscopic properties of the host galaxy are typical for a star formation- powered object. Using the observed value of the Balmer decrement, we derived the extinction in the galaxy's rest frame: A${}_V$åisebox-0.5ex 0.3+/-0.3 mag. Using three different star formation rate (SFR) indicators, we estimate SFRi̊sebox-0.5ex 10 M${}_{s}olar$ yr${}^{-}1$ or higher, depending on the extinction, with a lower limit of SFR>7 M${}_{s}olar$ yr${}^{-}1$. This is the highest value of the SFR measured for a GRB galaxy so far, and it gives some support to the idea that GRBs are closely related to massive star formation.

Based in part on observations obtained at the W. K. 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.