Abstract
The prompt γ-ray emission from γ-ray bursts (GRBs) should be detectable out to distances of z > 10 (ref. 1), and should therefore provide an excellent probe of the evolution of cosmic star formation, reionization of the intergalactic medium, and the metal enrichment history of the Universe1,2,3,4. Hitherto, the highest measured redshift for a GRB has been z = 4.50 (ref. 5). Here we report the optical spectrum of the afterglow of GRB 050904 obtained 3.4 days after the burst; the spectrum shows a clear continuum at the long-wavelength end of the spectrum with a sharp cut-off at around 9,000 Å due to Lyman α absorption at z ≈ 6.3 (with a damping wing). A system of absorption lines of heavy elements at z = 6.295 ± 0.002 was also detected, yielding the precise measurement of the redshift. The Si ii fine-structure lines suggest a dense, metal-enriched environment around the progenitor of the GRB.
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Acknowledgements
This work is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are grateful for support by the observatory. N.K. acknowledges support by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan and the Tokyo Tech COE-21 programme ‘Nanometer-scale Quantum Physics’. We thank S. Barthelmy for maintaining the GRB Coordinates Network, and the Swift team for providing rapid GRB localizations.
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Kawai, N., Kosugi, G., Aoki, K. et al. An optical spectrum of the afterglow of a γ-ray burst at a redshift of z = 6.295. Nature 440, 184–186 (2006). https://doi.org/10.1038/nature04498
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DOI: https://doi.org/10.1038/nature04498
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