Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Proton Cyclotron Features in Thermal Spectra of Ultra-magnetized Neutron
  Stars   A great deal of interest has been recently raised in connection with the
possibility that soft $\gamma$-ray repeaters (SGRs) and anomalous X-ray pulsars
(AXPs) contain {\em magnetars}, young neutron stars endowed with magnetic
fields $\gtrsim 10^{14}$ G. In this paper we calculate thermal spectra from
ultra-magnetized neutron stars for values of the luminosity and magnetic field
believed to be relevant to SGRs and AXPs. Emergent spectra are found to be very
close to a blackbody at the star effective temperature and exhibit a
distinctive absorption feature at the proton cyclotron energy $E_{c,p}\simeq
0.63 (B/10^{14} {\rm G})$ keV. The proton cyclotron features (PCFs) are
conspicuous (equivalent width of up to many hundreds eV) and relatively broad
($\Delta E/E \sim 0.05-0.2$). The detection of the PCFs is well within the
capabilities of present X-ray spectrometers, like the HETGS and METGS on board
Chandra. Their observation might provide decisive evidence in favor of the
existence of magnetars.

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The categories of this paper are: hep-th
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The categories of this paper are: physics
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The categories of this paper are: eess
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The categories of this paper are: funct-an
2
The categories of this paper are: math
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con
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The categories of this paper are: cond-mat
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat