Probing the complex environments of GRB host galaxies and intervening systems: high resolution spectroscopy of GRB050922C^*

¹ INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone (RM), Italy e-mail: piranomonte@oa-roma.inaf.it
² Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking Surrey, RH56NT, UK
³ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
⁴ School of Physical Sciences and NCPST, Dublin City University, Glasnevin, Dublin 9, Ireland
⁵ INAF-Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁶ Instituto de Astronomia, Universidad nacional Autonoma de Mexico, Apartado Postal 70-264, 04510 Mexico DF, Mexico
⁷ Università degli Studi di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
⁸ INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁹ International Center for Relativistic Astrophysics Network, 65122, Pescara, Italy
¹⁰ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, Place Jules Janssen, 92190 Meudon, France
¹² Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
¹³ NASA-Goddard Space Flight Center, Greenbelt, Maryland, 20771, USA
¹⁴ APC, Laboratoire Astroparticule et Cosmologie, UMR 7164, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France
¹⁵ CEA Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette, France
¹⁶ Dark Cosmology Centre, Niels Bohr Institute, Juliane Maries Vej 30, 2100 København Ø, Denmark

¹⁷ European Southern Observatory, Alonso de Córdova 3107, Santiago 19, Chile 

¹⁸ 
Instituto de Astronomía y Física del Espacio, CONICET/UBA, Casilla de Correos 67, Suc. 28, (1428) Buenos Aires, Argentina
¹⁹ JILA, Campus Box 440, University of Colorado, Boulder, CO 80309-0440, USA

Received: 7 November 2007
Accepted: 31 October 2008

Abstract

Aims. The aim of this paper is to investigate the environment of gamma ray bursts (GRBs) and the interstellar matter of their host galaxies.

Methods. To this purpose we use high resolution spectroscopic observations of the afterglow of GRB050922C, obtained with UVES/VLT ~ 3.5 h after the GRB event.

Results. We found that, as for most high resolution spectra of GRBs, the spectrum of the afterglow of GRB050922C is complex. At least seven components contribute to the main absorption system at . The detection of lines of neutral elements like MgI and the detection of fine-structure levels of the ions FeII, SiII and CII allows us to separate components in the GRB ISM along the line of sight. Moreover, in addition to the main system, we analyzed the five intervening systems between and identified along the GRB line of sight.

Conclusions. GRB afterglow spectra are very complex, but full of information. This can be used to disentangle the contribution of the different parts of the GRB host galaxy and to study their properties. Our metallicity estimates agree with the scenario of GRBs exploding in low metallicity galaxies