Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Neutron Star with a Carbon Atmosphere in the Cassiopeia A Supernova
  Remnant   The surface of hot neutron stars is covered by a thin atmosphere. If there is
accretion after neutron star formation, the atmosphere could be composed of
light elements (H or He); if no accretion takes place or if thermonuclear
reactions occur after accretion, heavy elements (for example, Fe) are expected.
Despite detailed searches, observations have been unable to confirm the
atmospheric composition of isolated neutron stars. Here we report an analysis
of archival observations of the compact X-ray source in the centre of the
Cassiopeia A supernova remnant. We show that a carbon atmosphere neutron star
(with low magnetic field) produces a good fit to the spectrum. Our emission
model, in contrast with others, implies an emission size consistent with
theoretical predictions for the radius of neutron stars. This result suggests
that there is nuclear burning in the surface layers and also identifies the
compact source as a very young (~330-year-old) neutron star.

2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
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The categories of this paper are: stat
30
The categories of this paper are: q-alg
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The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat