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 10⁵³ 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 ≈ 0.3±0.3 mag. Using three different star formation rate (SFR) indicators, we estimate SFR ≈ 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.