GRB 080913 at redshift 6.7

Understand

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 lambda = 9400 A, and zero flux for 7500 A < lambda<9400 A, which we interpret as the onset of a Gunn-Peterson trough at z=6.695+-0.025 (95.5% conf.
• level), making GRB 080913 the highest redshift GRB to date, and more distant than the highest-redshift QSO.
• We note that many redshift indicators which are based on promptly available burst or afterglow properties have failed for GRB 080913.