Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Orbital variability of the PSR J2051-0827 Binary System   We have carried out high-precision timing measurements of the binary
millisecond pulsar PSR J2051$-$0827 with the Effelsberg 100-m radio telescope
of the Max-Planck-Institut f\"ur Radioastronomie and with the Lovell 76-m radio
telescope at Jodrell Bank. The 6.5-yrs radio timing measurements have revealed
a significant secular variation of the projected semi-major axis of the pulsar
at a rate of $\dot x\equiv d(a_{\rm 1} \sin i)/dt = (-0.23\pm 0.03)\times
10^{-12}$, which is probably caused by the Newtonian spin-orbit coupling in
this binary system leading to a precession of the orbital plane. The required
misalignment of the spin and orbital angular momenta of the companion are
evidence for an asymmetric supernova explosion. We have also confirmed that the
orbital period is currently decreasing at a rate of $\dot P_{\rm b}=(-15.5 \pm
0.8)\times 10^{-12}$s s$^{-1}$ and have measured second and third orbital
period derivatives $d^2P_{\rm b}/dt^2=(+2.1 \pm 0.3)\times 10^{-20} {\rm
s^{-1}}$ and $d^3P_{\rm b}/dt^3 =(3.6 \pm 0.6)\times 10^{-28} {\rm s^{-2}}$,
which indicate a quasi-cyclic orbital period variation similar to those found
in another eclipsing pulsar system, PSR B1957+20. The observed variation of the
orbital parameters constrains the maximal value of the companion radius to
$R_{\rm c max} \sim 0.06 R_{\odot}$ and implies that the companion is
underfilling its Roche lobe by 50 %. The derived variation in the quadrupole
moment of the companion is probably caused by tidal dissipation similar to the
mechanism proposed for PSR B1957+20. We conclude that the companion is at least
partially non-degenerate, convective and magnetically active.

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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: nlin
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The categories of this paper are: bayes-an
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The categories of this paper are: adap-org
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The categories of this paper are: ao-sci
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The categories of this paper are: cs
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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: chem-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph