Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Thermal Composite Supernova Remnant Kes 27 as Viewed by CHANDRA:
  Shock Reflection from a Cavity Wall   We present a spatially resolved spectroscopic study of the thermal composite
supernova remnant Kes 27 with Chandra. The X-ray spectrum of Kes 27 is
characterized by K lines from Mg, Si, S, Ar, and Ca. The X-ray emitting gas is
found to be enriched in sulphur and calcium. The broadband and tri-color images
show two incomplete shell-like features in the northeastern half and brightness
fading with increasing radius in the southwest. There are over 30 unresolved
sources within the remnant. None show characteristics typical of young neutron
stars. The maximum diffuse X-ray intensity coincides with a radio bright region
along the eastern border. In general, gas in the inner region is at higher
temperature and emission is brighter than from the outer region. The gas in the
remnant appears to approach ionization equilibrium. The overall morphology can
be explained by the evolution of the remnant in an ambient medium with a
density enhancement from west to east. We suggest that the remnant was born in
a pre-existing cavity and that the inner bright emission is due to the
reflection of the initial shock from the dense cavity wall. This scenario may
provide a new candidate mechanism for the X-ray morphology of other thermal
composite supernova remnants.

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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
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The categories of this paper are: ao-sci
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The categories of this paper are: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: cs
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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: math