UVES/VLT high resolution absorption spectroscopy of the GRB 080330 afterglow: a study of the GRB host galaxy and intervening absorbers*
INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00044 Monteporzio Catone, Italy e-mail: email@example.com
2 JILA, Campus Box 440, University of Colorado, Boulder, CO 80309-0440, USA
3 Instituto de Astronomia, Universidad Nacional Autonomica de Mexico, Apartado Postal 70-264, 04510 Mexico DF, Mexico
4 University Paris 7, APC, Lab. Astroparticule et Cosmologie, UMR7164 CNRS, 10 rue Alice Domon et Lonie Duquet, 75205 Paris Cedex 13, France
5 INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
6 Laboratoire Astroparticule et Cosmologie, 10 rue A. Domon et L. Duquet, 75205 Paris Cedex 13, France
7 Service d'Astrophysique, DSM/DAPNIA/SAp, CEA-Saclay, 91191 Gif-sur-Yvette, France
8 School of Cosmic Physics, DIAS, 31 Fitzwilliam Place, Dublin 4, Ireland
9 School of Physical Sciences and NCPST, DCU, Glasnevin, Dublin 9, Ireland
10 Dunsink Observatory, Castleknock, Dublin 15, Ireland
Accepted: 15 May 2009
Aims. We study the gamma-ray burst (GRB) environment and intervening absorbers by analyzing the optical absorption features produced by gas surrounding the GRB or along its line of sight.
Methods. We analyzed high resolution spectroscopic observations (R = 40 000, = 3–6) of the optical afterglow of GRB 080330, taken with UVES at the VLT ~ 1.5 h after the GRB trigger.
Results. The spectrum illustrates the complexity of the ISM of the GRB host galaxy at which has at least four components in the main absorption system. We detect strong FeII, SiII, and NiII excited absorption lines associated with the bluemost component only. In addition to the host galaxy, at least two more absorbers lying along the line of sight to the afterglow have been detected in the redshift range , each exhibiting MgII absorption. For the bluemost component in the host galaxy, we derive information about its distance from the site of the GRB explosion. We do so by assuming that the excited absorption lines are produced by indirect UV pumping, and compare the data with a time dependent photo-excitation code. The distance of this component is found to be pc, which is lower than found for other GRBs (1–6 kpc). We identify two additional MgII absorbers, one of them with a rest frame equivalent width larger than 1 Å.
Conclusions. The distance between the GRB and the absorber measured in this paper confirms that the power of the GRB radiation can influence the conditions of the interstellar medium up to a distance of at least several hundred pc. For the intervening absorbers, we confirm the trend that on average one strong intervening system is found per afterglow, as has been noted in studies exhibiting an excess of strong MgII absorbers along GRB sightlines compared to quasars.
Key words: gamma rays: bursts / cosmology: observations / galaxies: abundances / ISM: general
© ESO, 2009