GRB 090417B AND ITS HOST GALAXY: A STEP TOWARD AN UNDERSTANDING OF OPTICALLY DARK GAMMA-RAY BURSTS
- Astrophysics Science Division, Code 660.1, 8800 Greenbelt Road Goddard Space Flight Centre, Greenbelt, MD 20771 (United States)
- INAF-IASF, Via Ugo La Malfa 153, I-90146 Palermo (Italy)
- Department of Astronomy, University of Texas, Austin, TX 78712 (United States)
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking Surrey RH5 6NT (United Kingdom)
- Dark Cosmology Centre, Niels Bohr Institutet, Koebenhavns Universitet, Juliane Maries Vej 30, DK-2100 Koebenhavn Oe (Denmark)
- Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, IS-107 (Iceland)
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden)
- Department of Astronomy and Astrophysics, Pennsylvania State University, 5252 Davey Lab, University Park, PA 16802 (United States)
GRB 090417B was an unusually long burst with a T{sub 90} duration of at least 2130 s and a multi-peaked light curve at energies of 15-150 keV. It was optically dark and has been associated with a bright star-forming galaxy at a redshift of 0.345 that is broadly similar to the Milky Way. This is one of the few cases where a host galaxy has been clearly identified for a dark gamma-ray burst (GRB) and thus an ideal candidate for studying the origin of dark bursts. We find that the dark nature of GRB 090417B cannot be explained by high redshift, incomplete observations, or unusual physics in the production of the afterglow. Assuming the standard relativistic fireball model for the afterglow we find that the optical flux is at least 2.5 mag fainter than predicted by the X-ray flux. The Swift/XRT X-ray data are consistent with the afterglow being obscured by a dense, localized sheet of dust approximately 30-80 pc from the burst along the line of sight. Our results suggest that this dust sheet imparts an extinction of A{sub V} {approx_gt} 12 mag, which is sufficient to explain the missing optical flux. GRB 090417B is an example of a GRBs that is dark due to the localized dust structure in its host galaxy.
- OSTI ID:
- 21452888
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 717; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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