GRB 051028: an intrinsically faint gamma-ray burst at high redshift?

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. (2006) GRB 051028: an intrinsically faint gamma-ray burst at high redshift? Astronomy and Astrophysics, 459 (3). pp. 763-767. ISSN 0004-6361

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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. 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. 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 vc 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.

Item Type:Article
Source:Copyright of this article belongs to EDP Sciences.
Keywords:Gamma Rays: Bursts; Techniques: Photometric; Cosmology: Observations
ID Code:100815
Deposited On:10 Dec 2016 12:31
Last Modified:10 Dec 2016 12:31

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