Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nature of the soft ULX in NGC 247: super-Eddington outflow and
  transition between the supersoft and soft ultraluminous regimes   We report on XMM-Newton/Chandra/Swift/HST observations of the ultraluminous
X-ray source (ULX) in NGC 247, which is found to make transitions between the
supersoft ultraluminous (SSUL) regime with a spectrum dominated by a cool
($\sim 0.1$ keV) blackbody component and the soft ultraluminous (SUL) regime
with comparable luminosities shared by the blackbody and power-law components.
Multi-epoch observations revealed an anti-correlation between the blackbody
radius and temperature, $R_{\rm bb} \propto T_{\rm bb}^{-2.8 \pm 0.3}$, ruling
out a standard accretion disk as the origin of the soft X-ray emission. The
soft X-ray emission is much more variable on both short and long timescales in
the SSUL regime than in the SUL regime. We suggest that the SSUL regime may be
an extension of the ultraluminous state toward the high accretion end, being an
extreme case of the SUL regime, with the blackbody emission arising from the
photosphere of thick outflows and the hard X-rays being emission leaked from
the embedded accretion disk via the central low-density funnel or advected
through the wind. However, the scenario that the supersoft ULXs are standard
ULXs viewed nearly edge-on cannot be ruled out. Flux dips on a timescale of 200
s were observed. The dips cannot be explained by an increase of absorption, but
could be due to the change of accretion rate or related to thermal fluctuations
in the wind or disk. The optical emission of NGC 247 ULX exhibits a blackbody
spectrum at a temperature of 19,000 K with a radius of 20 $R_\odot$, likely
arising from an OB supergiant companion star.

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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: econ
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: cmp-lg
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The categories of this paper are: cs
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an
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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: physics
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc