Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Troublesome Broadband Evolution of GRB 061126: Does a Grey Burst
  Imply Grey Dust?   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 seconds 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
spectral energy distribution 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 spectral energy distribution
provides no evidence of host-galaxy extinction, requiring either large
quantities of grey dust in the host system (at redshift 1.1588 +/- 0.0006,
based upon our late-time Keck spectroscopy) or separate physical origins for
the X-ray and optical afterglows.

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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
3
The categories of this paper are: physics
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The categories of this paper are: stat
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The categories of this paper are: supr-con
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: alg-geom
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The categories of this paper are: cmp-lg
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The categories of this paper are: chem-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: funct-an