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 gamma-ray burst (GRB) host. The implied isotropic gamma-ray energy release from the burst is in excess of 10(53) 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) approximate to 0.3 +/- 0.3 mag. Using three different star formation rate (SFR) indicators, we estimate SFR approximate to 10 M-. yr(-1) or higher, depending on the extinction, with a lower limit of SFR > 7 M-. 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.