Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: X-ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars
  Weakly Magnetized at Birth   The 105-ms X-ray pulsar J1852+0040 is the central compact object (CCO) in SNR
Kes 79. We report a sensitive upper limit on its radio flux density of 12 uJy
at 2 GHz using the NRAO GBT. Timing using XMM and Chandra over a 2.4 yr span
reveals no significant change in its spin period. The 2 sigma upper limit on
the period derivative leads, in the dipole spin-down formalism, to an energy
loss rate E-dot < 7e33 ergs/s, surface magnetic field strength B_p < 1.5e11 G,
and characteristic age tau_c = P/2P-dot > 8 Myr. This tau_c exceeds the age of
the SNR by 3 orders of magnitude, implying that the pulsar was born spinning at
its current period. However, the X-ray luminosity of PSR J1852+0040, L(bol) ~
3e33(d/7.1 kpc)^2 ergs/s is a large fraction of E-dot, which challenges the
rotation-powered assumption. Instead, its high blackbody temperature,
0.46+/-0.04 keV, small blackbody radius ~ 0.8 km, and large pulsed fraction, ~
80%, may be evidence of accretion onto a polar cap, possibly from a fallback
disk made of supernova debris. If B_p < 1e10 G, an accretion disk can penetrate
the light cylinder and interact with the magnetosphere while resulting torques
on the neutron star remain within the observed limits. A weak B-field is also
inferred in another CCO, the 424-ms pulsar 1E 1207.4-5209, from its steady spin
and soft X-ray absorption lines. We propose this origin of radio-quiet CCOs:
the B-field, derived from a turbulent dynamo, is weaker if the NS is formed
spinning slowly, which enables it to accrete SN debris. Accretion excludes
neutron stars born with both B_p < 1e11 G and P > 0.1 s from radio pulsar
surveys, where B_p < 1e11 G is not encountered except among very old (tau_c >
40 Myr) or recycled pulsars. Finally, such a CCO, if born in SN 1987A, could
explain the non-detection of a pulsar there.

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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: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: physics
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The categories of this paper are: adap-org
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The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: plasm-ph
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The categories of this paper are: supr-con
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The categories of this paper are: hep-th
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The categories of this paper are: q-bio