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Issue A&A
Volume 371, Number 1, May III 2001
Page(s) 52 - 60
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010311



A&A 371, 52-60 (2001)
DOI: 10.1051/0004-6361:20010311

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

S. Holland1, 2, J. P. U. Fynbo3, J. Hjorth4, J. Gorosabel5, H. Pedersen4, M. I. Andersen6, A. Dar7, B. Thomsen1, P. Møller3, G. Björnsson8, A. O. Jaunsen9, P. Natarajan10 and N. Tanvir11

1  Institute of Physics and Astronomy, University of Aarhus, 8000 Århus C., Denmark
    e-mail: bt@ifa.au.dk
2  Department of Physics, University of Notre Dame, Notre Dame, IN 46556-5670, USA
    e-mail: sholland@nd.edu
3  European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
    e-mail: jfynbo@eso.org; pmoller@eso.org
4  Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
    e-mail: jens@astro.ku.dk; holger@astro.ku.dk
5  Danish Space Research Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
    e-mail: jgu@dsri.dk
6  Division of Astronomy, University of Oulu, PO Box 3000, 90014 Oulu, Finland
    e-mail: manderse@sun3.oulu.fi
7  Department of Physics, Technion, Haifa 32000, Israel
    e-mail: arnon.dar@cern.ch
8  Science Institute, Dunhagi 3, University of Iceland, 107 Reykjavik, Iceland
    e-mail: gulli@raunvis.hi.is
9  European Southern Observatory, Casilla 19001, Santiago 19, Chile
    e-mail: ajaunsen@eso.org
10  Department of Astronomy, Yale University, New Haven, CT 06520-8181, USA
    e-mail: priya@astro.yale.edu
11  Department of Physical Sciences, University of Hertfordshire, College Lane, Hatfield, Hertfordshire, AL10 9AB, UK
    e-mail: nrt@star.herts.ac.uk

(Received 11 December 2000 / Accepted 27 February 2001 )

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 $\approx$ 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 R1/n profile with $n \approx 1.0$ and a half-light radius of $0\farcs13$ ( = 0.72 h100-1 proper kpc). This corresponds to an exponential disk with a scale radius of $0\farcs22$ ( = 1.21 h100-1 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.


Key words: supernovae: individual -- galaxies: individual -- galaxies: photometry -- galaxies: structure -- gamma rays: bursts

Offprint request: S. Holland, sholland@nd.edu

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© ESO 2001


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