Context. Thirteen years after the discovery of the first afterglows, the nature of dark gamma-ray bursts (GRB) still eludes explanation: while each long-duration GRB typically has an X-ray afterglow, optical/NIR emission is only seen for 40-60% of them. Aims: Here 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”. Methods: Observations were performed with the 7-channel “Gamma-Ray Optical and Near-infrared Detector” (GROND) at the 2.2 m MPI/ESO telescope. We used the afterglow detection rate in dependence on the delay time between GRB and the first GROND exposure. Results: 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. Conclusions: 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.
Greiner, J., Krühler, T., Klose, S., Afonso, P., Clemens, C., Filgas, R., et al. (2010). The nature of "dark" gamma-ray bursts. ASTRONOMY & ASTROPHYSICS, 526, A30.
|Citazione:||Greiner, J., Krühler, T., Klose, S., Afonso, P., Clemens, C., Filgas, R., et al. (2010). The nature of "dark" gamma-ray bursts. ASTRONOMY & ASTROPHYSICS, 526, A30.|
|Tipo:||Articolo in rivista - Articolo scientifico|
|Carattere della pubblicazione:||Scientifica|
|Titolo:||The nature of "dark" gamma-ray bursts|
|Autori:||Greiner, J; Krühler, T; Klose, S; Afonso, P; Clemens, C; Filgas, R; Hartmann, DH; Küpcü Yoldaş, A; Nardini, M; Olivares, EF; Rau, A; Rossi, A; Schady, P; Updike, A|
|Data di pubblicazione:||16-dic-2010|
|Rivista:||ASTRONOMY & ASTROPHYSICS|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1051/0004-6361/201015458|
|Appare nelle tipologie:||01 - Articolo su rivista|