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 overluminous galaxy with V_gal = 23.00 ± 0.10, (V - R)_gal = 0.43 ± 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 M_⊙ 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 ≈ 1.0 and a half-light radius of 0″.13 (= 0.72h₁₀₀^-1 proper kpc). This corresponds to an exponential disk with a scale radius of 0′.22 (= 1.21h₁₀₀^-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 α = -1.37±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.