Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An XMM-Newton observation of Ton S180: Constraints on the continuum
  emission in ultrasoft Seyfert galaxies   We present an XMM-Newton observation of the bright, narrow-line, ultrasoft
Seyfert 1 galaxy Ton S180. The 0.3-10 keV X-ray spectrum is steep and curved,
showing a steep slope above 2.5 keV (Gamma ~ 2.3) and a smooth, featureless
excess of emission at lower energies. The spectrum can be adequately
parameterised using a simple double power-law model. The source is strongly
variable over the course of the observation but shows only weak spectral
variability, with the fractional variability amplitude remaining approximately
constant over more than a decade in energy. The curved continuum shape and weak
spectral variability are discussed in terms of various physical models for the
soft X-ray excess emission, including reflection off the surface of an ionised
accretion disc, inverse-Compton scattering of soft disc photons by thermal
electrons, and Comptonisation by electrons with a hybrid thermal/non-thermal
distribution. We emphasise the possibility that the strong soft excess may be
produced by dissipation of accretion energy in the hot, upper atmosphere of the
putative accretion disc.

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The categories of this paper are: atom-ph
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The categories of this paper are: q-alg
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The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio
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The categories of this paper are: cond-mat
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: econ