Issue |
A&A
Volume 447, Number 3, March I 2006
|
|
---|---|---|
Page(s) | 897 - 903 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20054287 | |
Published online | 10 February 2006 |
A mean redshift of 2.8 for Swift gamma-ray bursts
1
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark e-mail: pallja@astro.ku.dk
2
Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB, UK
3
Lund Observatory, Box 43, 221 00 Lund, Sweden
4
Department of Astronomy, Yale University, PO Box 208101, New Haven CT 06520-8101, USA
5
Instituto de Astrofísica de Andalucía (CSIC), Apartado de Correos, 3004, 18080 Granada, Spain
6
Nordic Optical Telescope, Apartado de Correos, 474, 38700 Santa Cruz de la Palma (Tenerife), Spain
7
Joint Astronomy Centre, University Park, 660 North A'ohoku Place, Hilo, HI 96720, USA
8
Instituto de Astrofísica de Canarias, c/. Vía Láctea, s/n, 38200 La Laguna (Tenerife), Spain
9
Observatory, University of Helsinki, PO Box 14, 00014 University of Helsinki, Finland
10
Institute of Theoretical Physics and Astronomy, A. Gostauto St. 12, 01108 Vilnius, Lithuania
11
Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
12
Centro de Astrofísica Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
Received:
30
September
2005
Accepted:
21
October
2005
The exceptionally high luminosities of gamma-ray bursts (GRBs), gradually
emerging as extremely useful probes of star formation, make them promising
tools for exploration of the high-redshift Universe. Here we present a
carefully selected sample of Swift GRBs, intended to estimate in an
unbiased way the GRB mean redshift (), constraints on the
fraction of high-redshift bursts and an upper limit on the fraction of
heavily obscured afterglows. We find that
and that
at least 7% of GRBs originate at
. In addition, consistent with
pre-Swift observations, at most 20% of afterglows can be heavily
obscured. The redshift distribution of the sample is qualitatively consistent
with models where the GRB rate is proportional to the star formation rate in
the Universe. We also report optical, near-infrared and X-ray observations of
the afterglow of GRB 050814, which was seen to exhibit very red optical
colours. By modelling its spectral energy distribution we find that
. The high mean redshift of GRBs and their wide redshift
range clearly demonstrates their suitability as efficient probes of galaxies
and the intergalactic medium over a significant fraction of the history of
the Universe.
Key words: cosmology: observations / dust, extinction / early Universe / galaxies: high-redshift / gamma rays: bursts
© ESO, 2006
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