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We report on follow-up observations of the GRB 060927 using the ROTSE-IIIatelescope and a suite of larger aperture ground-based telescopes. An opticalafterglow was detected 20 s after the burst, the earliest rest-frame detectionof optical emission from any GRB. Spectroscopy performed with the VLT about 13hours after the trigger shows a continuum break at lambda ~ 8070 A produced byneutral hydrogen absorption at z~5.6. We also detect an absorption line at 8158A which we interpret as SiII at z=5.467. Hence, GRB 060927 is the second mostdistant GRB with a spectroscopically measured redshift. The shape of the redwing of the spectral break can be fitted by a damped Lyalpha profile with acolumn density with log(N_HI/cm^-2) ~ 22.5. We discuss the implications of thiswork for the use of GRBs as probes of the end of the dark ages and draw threemain conclusions: i) GRB afterglows originating from z>6 should be relativelyeasy to detect from the ground, but rapid NIR monitoring is necessary to ensurethat they are found; ii) The presence of large HI column densities in some GRBshost galaxies at z>5 makes the use of GRBs to probe the reionization epoch viaspectroscopy of the red damping wing challenging; iii) GRBs appear crucial tolocate typical star-forming galaxies at z>5 and therefore the type of galaxiesresponsible for the reionization of the universe.

Detection of GRB 060927 at z = 5.47: Implications for the Use of Gamma-Ray Bursts as Probes of the End of the Dark Ages