Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermal and Nonthermal Emission from the Forward Shock in Tycho's
  Supernova Remnant   We present Chandra X-ray images of Tycho's supernova remnant that delineate
its outer shock as a thin, smooth rim along the straight northeastern edge and
most of the circular western half. The images also show that the Si and S
ejecta are highly clumpy, and have reached near the forward shock at numerous
locations. Most of the X-ray spectra that we examine along the rim show
evidence of line emission from Si and S ejecta, while the continuum is
well-represented by either a thermal or nonthermal model. If the continuum is
assumed to be thermal, the electron temperatures at the rim are all similar at
about 2 keV, while the ionization ages are very low, because of the overall
weakness of the line emission. These electron temperatures are substantially
below those expected for equilibration of the electron and ion temperatures,
assuming shock velocities inferred from radio and X-ray expansion measurements;
the electron to mean temperature ratios are <~0.1-0.2, indicating that
collisionless heating of the electrons at the shock is modest. The nonthermal
contribution to these spectra may be important, but cannot be strongly
constrained by these data. It could account for as much as half of the flux in
the 4-6 keV energy range, based on an extrapolation of the hard X-ray spectrum
above 10 keV.

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The categories of this paper are: math-ph
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The categories of this paper are: q-alg
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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
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The categories of this paper are: physics
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: cs
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
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The categories of this paper are: hep-lat