Volume 583, November 2015
|Number of page(s)||10|
|Published online||30 October 2015|
Identifying the host galaxy of the short GRB 100628A⋆
1 Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
2 INAF-IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
3 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
4 Scottish Universities Physics Alliance for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK
5 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
6 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
7 Physics Department, University of Calabria, via P. Bucci, 87036 Arcavacata di Rende, Italy
8 Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, 306, Santiago 22, Chile
9 Millennium Institute of Astrophysics, Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
10 American River College, Physics and Astronomy Dpt., 4700 College Oak Drive, Sacramento, CA 95841, USA
11 Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
12 Institute of Experimental and Applied Physics, Czech Technical University in Prague, Horská 3a/22, 12800 Prague, Czech Republic
13 Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
14 European Southern Observatory, Alonso de Córdova 3107, 19001 Vitacura Casilla, Santiago 19, Chile
15 Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, Chile
16 Department of Chemistry and Physics, Roger Williams University, One Old Ferry Rd, Bristol, RI, 0209, USA
Received: 15 October 2014
Accepted: 15 August 2015
We report on the results of a comprehensive observing campaign to reveal the host galaxy of the short GRB 100628A. This burst was followed by a faint X-ray afterglow but no optical counterpart was discovered. However, inside the X-ray error circle a potential host galaxy at a redshift of z = 0.102 was soon reported in the literature. If this system is the host, then GRB 100628A was the cosmologically most nearby unambiguous short burst with a measured redshift so far. We used the multi-colour imager GROND at the ESO/La Silla MPG 2.2 m telescope, ESO/VLT spectroscopy, and deep Australia Telescope Compact Array (ATCA) radio-continuum observations together with publicly available Gemini imaging data to study the putative host and the galaxies in the field of GRB 100628A. We confirm that inside the X-ray error circle the most probable host-galaxy candidate is the morphologically disturbed, interacting galaxy system at z = 0.102. The interacting galaxies are connected by a several kpc long tidal stream, which our VLT/FORS2 spectroscopy reveals strong emission lines of [O ii], [O iii], Hα and Hβ, characteristic for the class of extreme emission-line galaxies and indicative of ongoing star formation. The latter leaves open the possibility that the GRB progenitor was a member of a young stellar population. However, we indentify a second host-galaxy candidate slightly outside the X-ray error circle. It is a radio-bright, luminous elliptical galaxy at a redshift z = 0.311. With a K-band luminosity of 2 × 1011L⊙ this galaxy resembles the probable giant elliptical host of the first well-localized short burst, GRB 050509B. If this is the host, then the progenitor of GRB 100628A was a member of an old stellar population.
Key words: gamma-ray burst: individual: 100628A
Based on observations collected at the Very Large Telescope of the European Southern Observatory, Paranal, Chile (ESO programme 087.D-0503 and 290.D-5194; PI: A. Nicuesa Guelbenzu; 090.A-0825; PI: D. Malesani), GROND (PI: J. Greiner), and ATCA (Program C2840; PI: A. Nicuesa Guelbenzu). Other observations are obtained from the Gemini and WISE Archive Facilities.
© ESO, 2015
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