Issue |
A&A
Volume 459, Number 3, December I 2006
|
|
---|---|---|
Page(s) | 763 - 767 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20054757 | |
Published online | 26 September 2006 |
GRB 051028: an intrinsically faint gamma-ray burst at high redshift?
1
Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 3.004, 18080 Granada, Spain e-mail: ajct@iaa.es
2
Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany
3
Max-Planck Institut für Astronomie, Koennigstuhl 17, 69117 Heidelberg, Germany
4
Indian Institute of Astrophysics, 560034 Bangalore, India
5
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
6
Instituto de Astrofísica de Canarias, via Láctea s/n, 38205 La Laguna, Tenerife, Spain
7
Laboratoire d'Astrophysique de Marseille, 13376 Marseille, France
8
Nikolaev State University, Nikolskaya 24, 54030 Nikolaev, Ukraine
9
American Association of Variable Star Observers, Cambridge, MA, USA
Received:
22
December
2005
Accepted:
14
September
2006
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 which is moving in a homogeneous
interstellar medium and with a cooling
frequency
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
is also consistent with the burst arising at high redshift,
compatible with the published pseudo-z of
.
Key words: gamma rays: bursts / techniques: photometric / cosmology: observations
© ESO, 2006
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