Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical Afterglow Observations of the Unusual Short-Duration Gamma-Ray
  Burst 040924   The 1-m telescope at Lulin Observatory and the 0.76-m Katzman Automatic
Imaging Telescope at Lick Observatory were used to observe the optical
afterglow of the short-duration (1.2--1.5 s) gamma-ray burst (GRB) 040924. This
object has a soft high-energy spectrum, thus making it an exceptional case,
perhaps actually belonging to the short-duration tail of the long-duration
GRBs. Our data, combined with other reported measurements, show that the early
R-band light curve can be described by two power laws with index alpha = -0.7
(at t = 16-50 min) and alpha = -1.06 (at later times). The rather small
difference in the spectral indices can be more easily explained by an afterglow
model invoking a cooling break rather than a jet break.

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The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas
1
The categories of this paper are: cs
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
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The categories of this paper are: acc-phys
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The categories of this paper are: dg-ga
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The categories of this paper are: math
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The categories of this paper are: mtrl-th
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: nucl-th
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The categories of this paper are: eess