The host galaxy and optical light curve of the gamma-ray burst GRB 980703
/ Authors
S. Holland, J. Fynbo, J. Hjorth, J. Gorosabel, H. Pedersen, M. Andersen, A. Dar, B. Thomsen, P. Møller, G. Bjornsson
and 12 more authors
A. Jaunsen, P. Natarajan, N. Aarhus, Notre Dame, Eső, Copenhagen, Dsri, Oulu, Technion, Iceland, Yale, Hertfordshire
/ 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 $V_{\rm gal} = 23.00 \pm 0.10$, ${(V-R)}_{\rm gal} = 0.43 \pm 0.13$, 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.
Journal: Astronomy and Astrophysics