Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Afterglow and Host Galaxy of GRB021004: A Comprehensive Study
  with the Hubble Space Telescope   (Abridged) We report on HST observations of the late-time afterglow and host
galaxy of GRB021004 (z=2.33). Although this GRB is one of the best observed so
far, there is substantial disagreement between different interpretations of
data sets on this burst in the literature. We have observed the field of
GRB021004 with the HST at multiple epochs from 3 days until almost 10 months
after the burst. With STIS spectroscopy we cover the spectral region 600-1700AA
in the restframe. From the limit on the flux recovery bluewards of the
Lyman-limit we constrain the HI column density to be above 1x10^18 cm-2 Based
on ACS and NICMOS imaging we find that the afterglow evolved achromatically
within the errors. The color changes observed by other authors during the first
four days must be related to a stochastic phenomenon superimposed on an
afterglow component with a constant spectral shape. This achromaticity implies
that the cooling break has remained on the blue side of the optical part of the
spectrum for at least two weeks after the burst. The optical-to-X-ray slope is
consistent with being the same at 1.4 and 52.4 days after the burst. This
indicates that the cooling frequency is constant and hence, according to
fireball models, that the circumburst medium has a constant density profile.
The late-time slope of the lightcurve is in the range alpha_2 = 1.8-1.9, and is
inconsistent with a single power-law. This could be due to a late-time
flattening caused by the transition to non-relativistic expansion or due to
excess emission (a lightcurve `bump') 7 days after burst. The host is a
starburst galaxy with no evidence for dust and with strong Ly-alpha emission.
The afterglow was located very close (~100 pc) to the center of the host
suggesting that the progenitor was associated with a circumnuclear starburst.

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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: hep-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
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The categories of this paper are: eess
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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: cs