Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The 35-day cycle in Her X-1 as observational appearance of freely
  precessing neutron star and forcedly precessing accretion disk   A careful analysis of X-ray light curves and pulse profiles of Her X-1
obtained over more than 20 years strongly evidences for free precession of a
magnetized neutron star with rotational axis inclined to the orbital plane as a
central clock underlying the observed 35-day period. Strong asymmetric X-ray
illumination of the optical star atmosphere leads to the formation of gaseous
streams coming out of the orbital plane and forming a tilted accretion disk
around the neutron star. Such a disk precesses due to tidal forces and
dynamical action of gaseous streams from the secondary companion. The locking
of these torques with neutron star precession makes the net disk precession
period to be very close to that of the neutron star free precession.

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The categories of this paper are: cs
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The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys