Bibcode
Jakobsson, P.; Levan, A.; Fynbo, J. P. U.; Priddey, R.; Hjorth, J.; Tanvir, N.; Watson, D.; Jensen, B. L.; Sollerman, J.; Natarajan, P.; Gorosabel, J.; Castro Cerón, J. M.; Pedersen, K.; Pursimo, T.; Árnadóttir, A. S.; Castro-Tirado, A. J.; Davis, C. J.; Deeg, H. J.; Fiuza, D. A.; Mikolaitis, S.; Sousa, S. G.
Bibliographical reference
Astronomy and Astrophysics, Volume 447, Issue 3, March I 2006, pp.897-903
Advertised on:
3
2006
Journal
Citations
266
Refereed citations
222
Description
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 (z_mean), constraints
on the fraction of high-redshift bursts and an upper limit on the
fraction of heavily obscured afterglows. We find that z_mean = 2.8 and
that at least 7% of GRBs originate at z > 5. 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 z = 5.3 ± 0.3. 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.