The host galaxy and optical light curve of the gamma-ray burst GRB 980703

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Abstract
We present deep HST/STIS and ground-based photometry of the host galaxy of the gamma-ray burst GRB 980703 taken 17, 551, 710, and 716 days after the burst. We find that the host is a blue, slightly over-luminous galaxy with , , and a centre that is ≈ 0.2 mag bluer than the outer regions of the galaxy. The galaxy has a star-formation rate of 8-13 , assuming no extinction in the host. We find that the galaxy is best fit by a Sersic profile with and a half-light radius of ( proper kpc). This corresponds to an exponential disk with a scale radius of ( proper kpc). Subtracting a fit with elliptical isophotes leaves large residuals, which suggests that the host galaxy has a somewhat irregular morphology, but we are unable to connect the location of GRB 980703 with any special features in the host. The host galaxy appears to be a typical example of a compact star forming galaxy similar to those found in the Hubble Deep Field North. The R-band light curve of the optical afterglow associated with this gamma-ray burst is consistent with a single power-law decay having a slope of . Due to the bright underlying host galaxy the late time properties of the light-curve are very poorly constrained. The decay of the optical light curve is consistent with a contribution from an underlying type Ic supernova like SN1998bw, or a dust echo, but such contributions cannot be securely established.
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