Paper: astro-ph/0509766
Date: Mon, 26 Sep 2005 18:35:18 GMT (21kb)

Title: GRB 050904 at redshift 6.3: observations of the oldest cosmic explosion
after the Big Bang

Authors: G. Tagliaferri, L.A. Antonelli, G. Chincarini, A. Fernandez-Soto, D.
Malesani, M. Della Valle, P. D'Avanzo, A. Grazian, V. Testa, S. Campana, S.
Covino, F. Fiore, L. Stella, et al

Categories: astro-ph

Comments: 2 figures, 5 pages, Submitted to A&A. Full author list in the paper
\\
We present optical and near-infrared observations of the afterglow of the
gamma-ray burst GRB 050904. We derive a photometric redshift $z = 6.3$,
estimated by the presence of the Lyman break falling between the $I$ and $J$
filters. This is by far the most distant GRB known to date. Its
isotropic-equivalent energy is $3.4 \times 10^{53}$ erg in the rest-frame
110-1100 keV energy band. Despite the high redshift, both the prompt and the
afterglow emission are not peculiar with respect to other GRBs. We find a break
in the $J$-band lightcurve at $t_{\rm b} = 2.6 \pm 1.0$ d. If we assume this is
the jet break we derive $E_{\rm jet} \gsim 5 \times 10^{51}$ erg. Our limits
show that GRB 050904 is consistent with the Amati and Ghirlanda relations. This
detection is consistent with the expected number of GRBs at $z > 6$ and shows
that GRBs are a powerful tool to study the star formation history up to very
high redshift.

\\ ( http://arXiv.org/abs/astro-ph/0509766 , 21kb)