The nature of dark gamma-ray bursts

J. Greiner, T. Krühler, S. Klose, P. Afonso, C. Clemens, R. Filgas, D. H. Hartmann, A. Yoldaş, M. Nardini, F. E. Olivares

Abstract

We use the afterglow detection statistics of the systematic follow‐up observations performed with GROND since mid‐2007 in order to derive the fraction of "dark bursts" according to different methods, and to distinguish between various scenarios for "dark bursts". For long‐duration Swift bursts with a detected X‐ray afterglow, we achieve a 90% (35/39) detection rate of optical/NIR afterglows whenever our observations started within less than 240 min after the burst. Complementing our GROND data with Swift/XRT spectra we construct broad‐band spectral energy distributions and derive rest‐frame extinctions. We detect 25–40% "dark bursts", depending on the definition used. The faint optical afterglow emission of "dark bursts" is mainly due to a combination of two contributing factors: (i) moderate intrinsic extinction at moderate redshifts, and (ii) about 22% of "dark" bursts at redshift >5.

Locations

• AIP conference proceedings - View - PDF
• arXiv (Cornell University) - View - PDF
• Springer Link (Chiba Institute of Technology) - View - PDF