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

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 3.4 × 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 light curve at tb = 2.6 ± 1.0 d (observer frame). If we assume this is the jet break, we derive a beaming-corrected energy Eγ ∼ (4 ÷ 12) × 10 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.

[1]  A. Fernandez-Soto,et al.  A New Catalog of Photometric Redshifts in the Hubble Deep Field , 1999 .

[2]  K. Pedersen,et al.  A very energetic supernova associated with the γ-ray burst of 29 March 2003 , 2003, Nature.

[3]  E. Bertin,et al.  SExtractor: Software for source extraction , 1996 .

[4]  J. Ostriker,et al.  Reionization of the Universe and the Early Production of Metals , 1996, astro-ph/9612127.

[5]  Alan A. Wells,et al.  The Swift Gamma-Ray Burst Mission , 2004, astro-ph/0405233.

[6]  Warren R. Brown,et al.  Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329 , 2003, astro-ph/0304173.

[7]  S. Covino,et al.  A Flash in the Dark: UVES Very Large Telescope High-Resolution Spectroscopy of Gamma-Ray Burst Afterglows , 2004, astro-ph/0409717.

[8]  A. Fontana,et al.  Photometric Redshifts and Selection of High-Redshift Galaxies in the NTT and Hubble Deep Fields , 2000, astro-ph/0009158.

[9]  G. Ghirlanda,et al.  The Collimation-corrected Gamma-Ray Burst Energies Correlate with the Peak Energy of Their νFν Spectrum , 2004, astro-ph/0405602.

[10]  Robert H. Becker,et al.  Evolution of the ionizing background and the epoch of reionization from the spectra of z ∼ 6 quasars , 2001 .

[11]  Andrei Mesinger,et al.  Constraints on the Small-Scale Power Spectrum of Density Fluctuations from High-Redshift Gamma-Ray Bursts , 2005, astro-ph/0501233.

[12]  A. Mazure,et al.  A large population of galaxies 9 to 12 billion years back in the history of the Universe , 2005, Nature.

[13]  N. Gehrels.  Confidence limits for small numbers of events in astrophysical data , 1986 .

[14]  Jorick S. Vink,et al.  On the metallicity dependence of Wolf-Rayet winds , 2005 .

[15]  R. Kudritzki.  Line-driven Winds, Ionizing Fluxes, and Ultraviolet Spectra of Hot Stars at Extremely Low Metallicity. I. Very Massive O Stars , 2002, astro-ph/0205210.

[16]  Donald Q. Lamb,et al.  Gamma-Ray Bursts as a Probe of the Very High Redshift Universe , 2000 .

[17]  M. Feroci,et al.  Intrinsic spectra and energetics of BeppoSAX Gamma-Ray Bursts with known redshifts , 2002, astro-ph/0205230.

[18]  Edward J. Wollack,et al.  First year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Determination of cosmological parameters , 2003, astro-ph/0302209.

[19]  M. C. Begam,et al.  An unusual supernova in the error box of the γ-ray burst of 25 April 1998 , 1998, Nature.

[20]  L. A. Antonelli,et al.  SN 2003lw and GRB 031203: A Bright Supernova for a Faint Gamma-Ray Burst , 2004, astro-ph/0405449.

[21]  Baltimore,et al.  The potential of INTEGRAL for the detection of high redshift GRBs , 2004 .

[22]  Bing Zhang,et al.  Gamma-Ray Bursts: Progress, Problems & Prospects , 2004 .