Document Type
Article
Publication Date
11-1-2007
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 ground-based 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 hr after the trigger shows a continuum break at λ ≈ 8070 Å, produced by neutral hydrogen absorption at z ≈ 5.6. We also detect an absorption line at 8158 Å, which we interpret as Si II λ1260 at z = 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 Lyα profile with a column density with log (NH /cm-2) = 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: (1) GRB afterglows originating from z ≳ 6 should be relatively easy to detect from the ground, but rapid near-infrared monitoring is necessary to ensure that they are found; (2) the presence of large H I column densities in some GRB host galaxies at z > 5 makes the use of GRBs to probe the reionization epoch via spectroscopy of the red damping wing challenging; and (3) GRBs appear crucial to locate typical star-forming galaxies at z > 5, and therefore the type of galaxies responsible for the reionization of the universe. © 2007. The American Astronomical Society. All rights reserved.
Publication Source (Journal or Book title)
Astrophysical Journal
First Page
1
Last Page
9
Recommended Citation
Ruiz-Velasco, A., Swan, H., Troja, E., Malesani, D., Fynbo, J., Starling, R., Xu, D., Aharonian, F., Akerlof, C., Andersen, M., Ashley, M., Barthelmy, S., Bersier, D., Castro, J., Castro-Tirado, A., Gehrels, N., Göǧüş, E., Gorosabel, J., Guidorzi, C., Güver, T., Hjorth, J., Horns, D., Huang, K., Jakobsson, P., Jensen, B., Kiziloǧlu, Ü., Kouveliotou, C., Krimm, H., Ledoux, C., Levan, A., Marsh, T., McKay, T., & Melandri, A. (2007). 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. Astrophysical Journal, 669 (1), 1-9. https://doi.org/10.1086/521546