Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Middle aged $\gamma$-ray pulsar J1957+5033 in X-rays: pulsations,
  thermal emission and nebula   We analyze new XMM-Newton and archival Chandra observations of the
middle-aged $\gamma$-ray radio-quiet pulsar J1957+5033. We detect, for the
first time, X-ray pulsations with the pulsar spin period of the point-like
source coinciding by position with the pulsar. This confirms the pulsar nature
of the source. In the 0.15--0.5 keV band, there is a single pulse per period
and the pulsed fraction is $\approx18\pm6$ per cent. In this band, the pulsar
spectrum is dominated by a thermal emission component that likely comes from
the entire surface of the neutron star, while at higher energies ($\gtrsim0.7$
keV) it is described by a power law with the photon index $\Gamma \approx 1.6$.
We construct new hydrogen atmosphere models for neutron stars with dipole
magnetic fields and non-uniform surface temperature distributions with
relatively low effective temperatures. We use them in the spectral analysis and
derive the pulsar average effective temperature of $\approx(2-3)\times10^5$ K.
This makes J1957+5033 the coldest among all known thermally emitting neutron
stars with ages below 1 Myr. Using the interstellar extinction--distance
relation, we constrain the distance to the pulsar in the range of 0.1--1 kpc.
We compare the obtained X-ray thermal luminosity with those for other neutron
stars and various neutron star cooling models and set some constraints on
latter. We observe a faint trail-like feature, elongated $\sim 8$ arcmin from
J1957+5033. Its spectrum can be described by a power law with a photon index
$\Gamma=1.9\pm0.5$ suggesting that it is likely a pulsar wind nebula powered by
J1957+5033.

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The categories of this paper are: physics
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The categories of this paper are: q-fin
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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: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: comp-gas
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The categories of this paper are: supr-con
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The categories of this paper are: stat
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph