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The troublesome broadband evolution of GRB 061126: Does a gray burst imply gray dust?

Perley, DA and Bloom, JS and Butler, NR and Pollack, LK and Holtzman, J and Blake, CH and Kocevski, D and Vestrand, WT and Li, W and Foley, RJ and Bellm, E and Chen, HW and Prochaska, JX and Starr, D and Filippenko, AV and Falco, EE and Szentgyorgyi, AH and Wren, J and Wozniak, PR and White, R and Pergande, J (2008) The troublesome broadband evolution of GRB 061126: Does a gray burst imply gray dust? The Astrophysical Journal, 672 (1). pp. 449-464. ISSN 1538-4357

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Abstract

We report on observations of a gamma-ray burst (GRB 061126) with an extremely bright (R ≈ 12 mag at peak) early-time optical afterglow. The optical afterglow is already fading as a power law 22 s after the trigger, with no detectable prompt contribution in our first exposure, which was coincident with a large prompt-emission gamma-ray pulse. The optical-infrared photometric SED is an excellent fit to a power law, but it exhibits a moderate red-to-blue evolution in the spectral index at about 500 s after the burst. This color change is contemporaneous with a switch from a relatively fast decay to slower decay. The rapidly decaying early afterglow is broadly consistent with synchrotron emission from a reverse shock, but a bright forward-shock component predicted by the intermediate- to late-time X-ray observations under the assumptions of standard afterglow models is not observed. Indeed, despite its remarkable early-time brightness, this burst would qualify as a dark burst at later times on the basis of its nearly flat optical-to-X-ray spectral index. Our photometric SED provides no evidence of host galaxy extinction, requiring either large quantities of gray dust in the host system (at redshift 1.1588 ± 0.0006, based on our late-time Keck spectroscopy) or separate physical origins for the X-ray and optical afterglows. © 2008. The American Astronomical Society. All rights reserved.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Q Science > QD Chemistry
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
Date Deposited: 23 May 2017 10:21
Last Modified: 13 Sep 2017 03:02
DOI or Identification number: 10.1086/523929
URI: http://researchonline.ljmu.ac.uk/id/eprint/6507

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