Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Early Optical Afterglow of GRB 030418 and Progenitor Mass Loss   The ROTSE-IIIa telescope and the SSO-40 inch telescope, both located at
Siding Spring Observatory, imaged the early time afterglow of GRB 030418. In
this report we present observations of the early afterglow, first detected by
the ROTSE-IIIa telescope 211 s after the start of the burst, and only 76 s
after the end of the gamma-ray activity. We detect optical emission that rises
for ~600 s, slowly varies around R=17.3 mag for ~1400 s, and then fades as a
power law of index alpha=-1.36. Additionally, the ROTSE-IIIb telescope, located
at McDonald Observatory, imaged the early time afterglow of GRB 030723. The
behavior of this light curve was qualitatively similar to that of GRB 030418,
but two magnitudes dimmer. These two afterglows are dissimilar to other
afterglows such as GRB 990123 and GRB 021211. We investigate whether the early
afterglow can be attributed to a synchrotron break in a cooling synchrotron
spectrum as it passes through the optical band, but find this model is unable
to accurately describe the early light curve. We present a simple model for
gamma-ray burst emission emerging from a wind medium surrounding a massive
progenitor star. This model provides an effective description of the data, and
suggests that the rise of the afterglow can be ascribed to extinction in the
local circumburst environment. In this interpretation, these events provide
further evidence for the connection between gamma-ray bursts and the collapse
of massive stars.

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The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
3
The categories of this paper are: physics
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph