An HST study of three very faint GRB host galaxies ^*

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: ajaunsen@eso.org
² Division of Astronomy, PO Box 3000, 90014 University of Oulo, Finland e-mail: michael.andersen@oulo.fi
³ Astrophysikalische Institut Potsdam, An der Sterwarte 16, 14482 Potsdam, Germany e-mail: mandersen@aip.de
⁴ Astronomical Observatory, University of Copenhagen, 2100 Copenhagen Ø, Denmark e-mail: jens@astro.ku.dk
⁵ Department of Physics and Astronomy, University of Aarhus, 8000 Århus C, Denmark e-mail: jfynbo@phys.au.dk, bt@phys.au.dk
⁶ Department of Physics, University of Notre Dame, Notre Dame, IN 46556–5670, USA e-mail: sholland@nd.edu
⁷ Danish Space Research Institute Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark e-mail: jgu@dsri.dk
⁸ Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain e-mail: jgu@iaa.es
⁹ Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), PO Box 50727, 28080, Madrid, Spain e-mail: jgu@laeff.esa.es
¹⁰ University of Texas, Department of Astronomy, C-1400, Austin, TX–78712, USA e-mail: schaefer@astro.as.utexas.edu
¹¹ Science Institute, Dunhagi 3, University of Iceland 107 Reykjavik, Iceland e-mail: gulli@raunvis.hi.is
¹² Department of Astronomy, Yale University, 265 Whitney Avenue, New Haven, CT 06511, USA e-mail: priya@astro.yale.edu
¹³ Department of Physical Sciences, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK e-mail: nrt@star.herts.ac.uk

Corresponding author: A. O. Jaunsen, ajaunsen@eso.org

Received: 16 April 2002
Accepted: 28 January 2003

Abstract

As part of the HST/STIS GRB host survey program we present the detection of three faint gamma-ray burst (GRB) host galaxies based on an accurate localisation using ground-based data of the optical afterglows (OAs). A common property of these three hosts is their extreme faintness. The location at which GRBs occur with respect to their host galaxies and surrounding environments are robust indicators of the nature of GRB progenitors. The bursts studied here are among the four most extreme outliers, in terms of relative distance from the host center, in the recent comprehensive study of Bloom et al. ([CITE]). We obtain a revised and much higher probability that the galaxies identified as hosts indeed are related to the GRBs (, following Bloom et al. [CITE]), thereby strengthening the conclusion that GRBs are preferentially located in star-forming regions in their hosts. Apart from being faint, the three hosts consist of multiple structures, indicative of merging and active star-formation. For one of the hosts, GRB 980329, we estimate a photometric redshift of .