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

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 hardX-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 Reflection Grating Spectrometer (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 broad-band 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 (kT(e) similar to 0.3 keV) and optically thick (tau similar to 10) corona, mostly contributing to the soft X-rays; (c) Comptonization by a standard hot (kT(e) greater than or similar to 100 keV) and optically thin (tau < 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-hot less than or similar to R-warm less than or similar to 10 r(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. 3.1 sigma significance) evidence of which is indeed found in the RGS spectrum.