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

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 $V_{\rm gal} = 23.00 \pm 0.10$, ${(V-R)}_{\rm gal} = 0.43 \pm 0.13$, 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 $\mathcal{M}_{\odot} {\rm yr}^{-1}$, assuming no extinction in the host. We find that the galaxy is best fit by a Sersic $R^{1/n}$ profile with $n \approx 1.0$ and a half-light radius of $0\farcs13$ ($= 0.72 h_{100}^{-1}$ proper kpc). This corresponds to an exponential disk with a scale radius of $0\farcs22$ ($= 1.21 h_{100}^{-1}$ 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 $\alpha = -1.37 \pm 0.14$. 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.