The first broad-band X-ray view of the narrow-line Seyfert 1 Ton S180

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Abstract
We present joint XMM-Newton and NuSTAR observations of the ‘bare’ narrow line Seyfert 1 Ton S180 (z = 0.062), carried out in 2016 and providing the first hard X-ray view of this luminous galaxy. We find that the 0.4–30 keV band cannot be self-consistently reproduced by relativistic reflection models, which fail to account simultaneously for the soft and hard X-ray emission. The smooth soft excess prefers extreme blurring parameters, confirmed by the nearly featureless nature of the RGS spectrum, while the moderately broad Fe K line and the modest hard excess above 10 keV appear to arise in a milder gravity regime. By allowing a different origin of the soft excess, the broadband X-ray spectrum and overall spectral energy distribution (SED) are well explained by a combination of: (a) direct thermal emission from the accretion disc, dominating from the optical to the far/extreme UV; (b) Comptonization of seed disc photons by a warm (kTe ∼ 0.3 keV) and optically thick (τ ∼ 10) corona, mostly contributing to the soft X-rays; (c) Comptonization by a standard hot (⁠|$kT_{\rm e}\gtrsim 100$| keV) and optically thin (τ < 0.5) corona, responsible for the primary X-ray continuum; and (d) reflection from the mid/outer part of the disc. The two coronae are suggested to be rather compact, with |$R_{\rm hot}\lesssim R_{\rm warm}\lesssim 10\, r_{\rm g}$|⁠. Our SED analysis implies that Ton S180 accretes at super-Eddington rates. This is a key condition for the launch of a wind, marginal (i.e., 3.1σ significance) evidence of which is indeed found in the RGS spectrum.
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Funding Information
  • Ecological Society of America
  • National Aeronautics and Space Administration
  • California Institute of Technology
  • Jet Propulsion Laboratory
  • Horizon 2020 (664931)
  • Istituto Nazionale di Astrofisica
  • European Research Council (340442)
  • Centre National d’Etudes Spatiales

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