Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fe K$\alpha$ and Fe K$\beta$ line detection in the NuSTAR spectrum of
  the ultra-bright Z-source Scorpius X-1   Low-mass X-ray binaries hosting a low-magnetised neutron star, which accretes
matter via Roche-lobe overflow, are generally grouped in two classes, named
Atoll and Z sources after the path described in their X-ray colour-colour
diagrams. Scorpius X-1 is the brightest persistent low-mass X-ray binary known
so far, and it is the prototype of the Z sources. We analysed the first NuSTAR
observation of this source to study its spectral emission exploiting the high
statistics data collected by this satellite. Examining the colour-colour
diagram, the source was probably observed during the lower normal and flaring
branches of its Z-track. We separated the data from the two branches in order
to investigate the evolution of the source along the track. We fitted the 3-60
keV NuSTAR spectra using the same models for both the branches. We adopted two
description for the continuum: in the first case we used a blackbody and a
thermal Comptonisation with seed photons originating in the accretion disc; in
the second one, we adopted a disc-blackbody and a Comptonisation with a
blackbody-shaped spectrum of the incoming seed photons. A power-law fitting the
high energy emission above 20 keV was also required in both cases. The two
models provide the same physical scenario for the source in both the branches:
a blackbody temperature between 0.8 and 1.5 keV, a disc-blackbody with
temperature between 0.4 and 0.6 keV, and an optically thick Comptonising corona
with optical depth between 6 and 10 and temperature about 3 keV. Furthermore,
two lines related to the K$\alpha$ and K$\beta$ transitions of the He-like Fe
XXV ions were detected at 6.6 keV and 7.8 keV, respectively. A hard tail
modelled by a power law with a photon index between 2 and 3 was also required
for both the models.

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The categories of this paper are: hep-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
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The categories of this paper are: stat
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
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The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: acc-phys