Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An Halpha nebula possibly associated with the central X-ray source in
  the G 266.1-1.2 supernova remnant   We report the discovery of a small Halpha nebula positionally coincident with
the candidate neutron star AX J0851.9-4617.4 located at the center of the
supernova remnant G 266.1-1.2. The nebula has a roughly circular shape with a
diameter of ~6'' and a flux of ~10^-2 photons cm^-2 s^-1 in the Halpha line.
Considering the uncertainties in the distance and energy output from the
putative neutron star, we find that such a flux can be explained either in a
bow-shock model or assuming that the nebular emission is due to
photo-ionization and heating of the ambient gas.

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The categories of this paper are: gr-qc
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The categories of this paper are: atom-ph
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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: math
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The categories of this paper are: econ
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The categories of this paper are: alg-geom
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The categories of this paper are: cs
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The categories of this paper are: comp-gas
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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: acc-phys
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: adap-org