Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral and Temporal Properties of Ultra-luminous X-ray Source NGC 55
  ULX1   We investigate the spectral and temporal properties of ultra-luminous X-ray
source (ULX) NGC~55~ULX1 using {\it Swift}, {\it XMM-Newton} and {\it NuSTAR}
observations conducted during 2013--2021. In these observations, the source
flux varies by a factor of $\sim 5-6$, and we identify the source mainly in the
$soft~ultraluminous$ (SUL) state of ULXs. We fit the X-ray spectra with a two
thermal component model consisting of a blackbody (for the soft component) and
a disc (for the hard component), and the soft component dominates in these
observations. The soft component in the SUL state shows properties similar to
that of ultraluminous supersoft sources, for example, an anti-correlation
between the characteristic radius and temperature of the blackbody component.
In addition, we observe a positive correlation between the blackbody and inner
disc temperatures when the X-ray spectra are fitted with the two-thermal
component model. The source exhibits marginal evidence of X-ray flux dips in
the {\it Swift} and {\it XMM-Newton} observations at different intensity
levels. We explain the observed spectral and temporal properties of the source
by invoking the supercritical radiatively driven outflow mechanism.

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The categories of this paper are: solv-int
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: atom-ph
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The categories of this paper are: math
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The categories of this paper are: mtrl-th
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The categories of this paper are: adap-org
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: cmp-lg
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The categories of this paper are: cond-mat
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con