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

D. A. Perley, J. S. Bloom, N. R. Butler, L. K. Pollack, J. Holtzman, C. H. Blake, D. Kocevski, W. T. Vestrand, W. Li, R. J. Foley, E. Bellm, H. W. Chen, J. X. Prochaska, D. Starr, A. V. Filippenko, E. E. Falco, A. H. Szentgyorgyi, J. Wren, P. R. Wozniak, R. WhiteJ. Pergande

Research output: Contribution to journalArticlepeer-review

103 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)449-464
Number of pages16
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 1 2008
Externally publishedYes


  • Gamma rays: bursts

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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