학술논문
Detection of GRB 060927 at zeta = 5.47: Implications for the Use of Gamma-Ray Bursts as Probes of the End of the Dark Ages
Document Type
Report
Author
Ruiz-Velasco, A. E; Swan, H; Troja, E; Malesani, D; Fynbo, J. P. U; Sterling, R. L. C; Xu, D; Aharonian, F; Akerlof, C; Andersen, M. I; Ashley, M. C. B; Barthelmy, S. D; Bersier, D; CastroCeron, J. M; Castro-Tirado, A. J; Gehrels, N; Gogus, E; Gorosabel, J; Guidorzi, C; Guver, T; Hjorth, J; Horns, D; Huang, K. Y; Jakobsson, P; Jensen, B. L
Source
Subject
Language
English
Abstract
We report on follow-up observations of the gamma-ray burst GRB 060927 using the robotic ROTSE-IIIa telescope and a suite of larger aperture groundbased telescopes. An optical afterglow was detected 20 s after the burst, the earliest rest-frame detection of optical emission from any GRB. Spectroscopy performed with the VLT about 13 hours after the trigger shows a continuum break at lambda approx. equals 8070 A, produced by neutral hydrogen absorption at zeta = 5.6. We also detect an absorption line at 8158 A which we interpret as Si II lambda 1260 at zeta = 5.467. Hence, GRB 060927 is the second most distant GRB with a spectroscopically measured redshift. The shape of the red wing of the spectral break can be fitted by a damped Ly(alpha) profile with a column density with log(N(sub HI)/sq cm) = 22.50 +/- 0.15. We discuss the implications of this work for the use of GRBs as probes of the end of the dark ages and draw three main conclusions: i) GRB afterglows originating from zeta greater than or approx. equal to 6 should be relatively easy to detect from the ground, but rapid near-infrared monitoring is necessary to ensure that they are found; ii) The presence of large H I column densities in some GRBs host galaxies at zeta > 5 makes the use of GRBs to probe the reionization epoch via spectroscopy of the red damping wing challenging; iii) GRBs appear crucial to locate typical star-forming galaxies at zeta > 5 and therefore the type of galaxies responsible for the reionization of the universe.