Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A broad absorption feature in the X-ray spectrum of the isolated neutron
  star RBS1223 (1RXS J130848.6+212708)   X-ray spectra of the isolated neutron star RBS1223 obtained with the
instruments on board XMM-Newton in December 2001 and January 2003 show
deviations from a Planckian energy distribution at energies below 500 eV. The
spectra are well fit when a broad, Gaussian-shaped absorption line with sigma =
100 eV and centered at an energy of 300 eV is added to an absorbed blackbody
model. The resulting equivalent width of the line is -150 eV. However, the
spectral resolution at these low energies of the EPIC detectors and the lower
statistical quality and restricted energy band of the RGS instruments are not
sufficient to exclude even broader lines at energies down to 100 eV or several
unresolved lines. The most likely interpretation of the absorption feature is a
cyclotron absorption line produced by protons in the magnetic field of the
neutron star. In this picture line energies of 100-300 eV yield a magnetic
field strength of 2-6x10^13 G for a neutron star with canonical mass and
radius. Folding light curves from different energy bands at a period of 10.31
s, which implies a double peaked pulse profile, shows different hardness ratios
for the two peaks. This confirms that the true spin period of RBS1223 is twice
as long as originally thought and suggests variations in cyclotron absorption
with pulse phase. We also propose that changes in photo-electric absorption
seen in phase resolved spectra of RX J0720.4-3125 by Cropper et al. (2001),
when formally fit with an absorbed blackbody model, are caused instead by
cyclotron absorption varying with pulse phase.

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The categories of this paper are: math
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The categories of this paper are: comp-gas
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The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-bio
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The categories of this paper are: stat
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The categories of this paper are: funct-an
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The categories of this paper are: acc-phys
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The categories of this paper are: eess