Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Small-Scale X-ray Variability in the Cassiopeia A Supernova Remnant   A comparison of X-ray observations of the Cassiopeia A supernova remnant
taken in 2000, 2002, and 2004 with the Chandra ACIS-S3 reveals the presence of
several small scale features (<= 10 arcsec) which exhibit significant intensity
changes over a 4 year time frame. Here we report on the variability of six
features, four of which show count rate increases from ~ 10% to over 90%, and
two which show decreases of ~ 30% -- 40%. While extracted 1-4.5 keV X-ray
spectra do not reveal gross changes in emission line strengths, spectral fits
using non-equilibrium ionization, metal-rich plasma models indicate increased
or decreased electron temperatures for features showing increasing or
decreasing count rates, respectively. Based on the observed count rate changes
and the assumption that the freely expanding ejecta has a velocity of ~ 5000
km/s at the reverse shock front, we estimate the unshocked ejecta to have
spatial scale variations of 0.02 - 0.03 pc, which is consistent with the X-ray
emitting ejecta belonging to a more diffuse component of the supernova ejecta
than that seen in the optically emitting ejecta, which have spatial scales ~
0.001 pc.

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The categories of this paper are: plasm-ph
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The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph