An XMM-Newton observation of Ton S180: Constraints on the continuum emission in ultrasoft Seyfert galaxies

Details An XMM-Newton observation of Ton S180: Constraints on the continuum emission in ultrasoft Seyfert galaxies An XMM-Newton observation of Ton S180: Constraints on the continuum emission in ultrasoft Seyfert galaxies

2002-07-30

arxiv.org/abs/astro-ph/0207650v1

Mon.Not.Roy.Astron.Soc.337:247,2002

Astronomy and Astrophysics

Astrophysics

9 pages, accepted for publication in MNRAS

Scientific paper

10.1046/j.1365-8711.2002.05908.x

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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