Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The neutron star in HESS J1731-347: CCOs as laboratories to study the
  equation of state of superdense matter   Context: Central Compact Objects (CCOs) in supernova remnants are isolated
thermally emitting neutron stars (NSs). They are most probably characterized by
a magnetic field strength that is roughly two orders of magnitude lower than
that of most of the radio and accreting pulsars. The thermal emission of CCOs
can be modeled to obtain constraints on the physical parameters of the star
such as its mass, radius, effective temperature, and chemical composition.
Aims: The CCO in HESS, J1731-347 is one of the brightest objects of this class.
We present our analysis of two new XMM-Newton observations of the source which
increase the total exposure time of the by a factor of five compared to the
analyses presented before. Methods: We use our numerical spectral models for
carbon and hydrogen atmospheres to fit the spectrum of the CCO. From our fits,
we derive constraints on the physical parameters of the emitting star. We also
use the new data to derive new upper limits on pulsations and to confirm the
absence of a long-term variability. Results: The analysis shows that atmosphere
spectral models are clearly preferred by the fit over the blackbody function.
Under the assumption that the X-ray emission is uniformly produced by the
entire star surface, hydrogen atmosphere models lead to uncomfortably large
distances of the CCO, above 7-8 kpc. On the other hand, the carbon atmosphere
model formally excludes distances above 5-6 kpc and is compatible with the
source located in the Scutum-Crux (3 kpc) or Norma-Cygnus (4.5 kpc) Galactic
spiral arm. We provide and discuss the corresponding confidence contours in the
NS mass-radius plane. The measured effective temperature indicates that the NS
is exceptionally hot for the estimated age of 30 kyr. We discuss possible
cooling scenarios to explain this property, as well as possible additional
constraints on the star mass and radius from cooling theory.

14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
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The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg