GRB 080913 at Redshift 6.7
Greiner, J.; McBreen, S.; Hartmann, D. H.; Vreeswijk, P. M.; Klose, S.; Gehrels, N.; Kawai, N.; Milvang-Jensen, B.; Schady, P.; Watson, D.; Fynbo, J. P. U.; Hasinger, G.; Krühler, T.; Filgas, R.; Clemens, C.; Kann, D. A.; Rossi, A.; Jehin, E.; Wiersema, K.; Beardmore, A. P.; Burrows, D. N.; Levan, A. J.; Zhang, B.; Oates, S. R.; Tanvir, N. R.; Malesani, D.; Hjorth, J.; Liang, E. W.; Mészáros, P.; Barthelmy, S. D.; Schulze, S.; Yoldaş, A.; Aoki, K.; Pierini, D.; Savaglio, S.; Ferrero, P.; Schwarz, R.; Pyo, T. -S.; Afonso, P.; Totani, T.; Wu, X. F.; Zhang, B. B.; Haiman, Z.; Szokoly, G.; Yoldaş, A. Küpcü; Toma, K.; Terada, K.
Germany, Denmark, United Kingdom, Japan, United States, China, Belgium, Hungary
Abstract
We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its high-z nature via the detection of a spectral break between the i' and z' bands. Spectroscopy obtained at the ESO-VLT revealed a continuum extending down to λ = 9400 Å, and zero flux for 7500 Å<λ < 9400 Å, which we interpret as the onset of a Gunn-Peterson trough at z = 6.695± 0.025 (95.5% confidence level), making GRB 080913 the highest-redshift gamma-ray burst (GRB) to date, and more distant than the highest-redshift QSO. We note that many redshift indicators that are based on promptly available burst or afterglow properties have failed for GRB 080913. We report on our follow-up campaign and compare the properties of GRB 080913 with bursts at lower redshift. In particular, since the afterglow of this burst is fainter than typical for GRBs, we show that 2 m class telescopes can identify most high-redshift GRBs.