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

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
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Abstract

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 from 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 3.4x10^53 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 light curve at t_b = 2.6 +- 1.0 d (observer frame). If we assume this is the jet break, we derive a beaming-corrected energy E_gamma = (4-12)x10^51 erg. This limit shows 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.

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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. 2005-10-06. GRB 050904 at redshift 6.3: observations of the oldest cosmic explosion after the Big Bang. https://doi.org/10.1051/0004-6361%3A200500196

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