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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 308814.0, MPI für Astronomie / Publikationen_mpia
GRB 051028: an intrinsically faint gamma-ray burst at high redshift?
Authors:Castro-Tirado, A. J.; Jelínek, M.; Pandey, S. B.; McBreen, S.; de Jong, J.; Sahu, D. K.; Ferrero, P.; Caballero, J. A.; Gorosabel, J.; Kann, D. A.; Klose, S.; de Ugarte Postigo, A.; Anupama, G. C.; Gry, C.; Guziy, S.; Srividya, S.; Valdivielso, L.; Vanniarajan, S.; Henden, A. A.
Date of Publication (YYYY-MM-DD):2006
Journal Abbrev.:Astronomy and Astrophysics
Start Page:763
End Page:767
Audience:Not Specified
Abstract / Description:Aims.We present multiwavelength observations of the gamma-ray burst GRB 051028 detected by HETE-2 in order to derive its afterglow emission parameters and to determine the reason for its optical faintness when compared to other events.<BR /> Methods: .Observations were taken in the optical (2.0 m Himalayan Chandra Telescope, 1.34 m Tautenburg, 4.2 m William Herschel Telescope) and in X-rays (Swift/XRT) between 2.7 h and ~10 days after the onset of the event.<BR /> Results: .The data can be interpreted by collimated emission in a jet with a typical value of p = 2.4 which is moving in a homogeneous interstellar medium and with a cooling frequency nuc still above the X-rays at 0.5 days after the burst onset. GRB 051028 can be classified as a "gray" or "potentially dark" GRB. On the basis of the combined optical and Swift/XRT data, we conclude that the reason for the optical dimness is not extra absorption in the host galaxy, but rather the GRB taking place at high-redshift. We also notice the very striking similarity with the optical lightcurve of GRB 050730, a burst with a spectroscopic redshift of 3.967, although GRB 051028 is ~3 mag fainter. We suggest that the bumps could be explained by multiple energy injection episodes and that the burst is intrinsically faint when compared to the average afterglows detected since 1997. The non-detection of the host galaxy down to R = 25.1 is also consistent with the burst arising at high redshift, compatible with the published pseudo-z of 3.7 ± 1.8.<BR />
Free Keywords:gamma rays: bursts; techniques: photometric; cosmology: observations
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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