Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A curious case of the accretion-powered X-ray pulsar GX 1+4   We present detailed spectral and timing studies using a NuSTAR observation of
GX 1+4 in October 2015 during an intermediate intensity state. The measured
spin period of 176.778 s is found to be one of the highest values since its
discovery. In contrast to a broad sinusoidal-like pulse profile, a peculiar
sharp peak is observed in profiles below ~25 keV. The profiles at higher
energies are found to be significantly phase-shifted compared to the soft X-ray
profiles. Broadband energy spectra of GX 1+4, obtained from NuSTAR and Swift
observations, are described with various continuum models. Among these, a two
component model consisting of a bremsstrahlung and a blackbody component is
found to best-fit the phase-averaged and phase-resolved spectra. Physical
models are also used to investigate the emission mechanism in the pulsar, which
allows us to estimate the magnetic field strength to be in
$\sim$(5-10)$\times$10$^{12}$ G range. Phase-resolved spectroscopy of NuSTAR
observation shows a strong blackbody emission component in a narrow pulse phase
range. This component is interpreted as the origin of the peculiar peak in the
pulse profiles below $\le$25 keV. The size of emitting region is calculated to
be $\sim$400 m. The bremsstrahlung component is found to dominate in hard
X-rays and explains the nature of simple profiles at high energies.

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The categories of this paper are: hep-lat
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
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The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol