Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cyclotron harmonics in opacities of isolated neutron star atmospheres   Some of X-ray dim isolated neutron stars (XDINS) and central compact objects
in supernova remnants (CCO) show absorption features in their thermal soft
X-ray spectra. It has been hypothesized that these features could be due to the
periodic peaks in free-free absorption opacities, caused by either Landau
quantization of electron motion in magnetic fields B<10^{11} G or analogous
quantization of ion motion in magnetic fields B>10^{13} G. Here, I review the
physics behind cyclotron quantum harmonics in free-free photoabsorption,
discuss different approximations for their calculation, and explain why the ion
cyclotron harmonics (beyond the fundamental) cannot be observed.

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The categories of this paper are: q-bio
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The categories of this paper are: acc-phys
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The categories of this paper are: econ
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: math-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: adap-org
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The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph