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

Abstract

We present joint \textit{XMM-Newton} and \textit{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 ($k{T}_{\mathrm{e}}\sim 0.3$ keV) and optically thick ($\ddot{I}„\sim 10$) corona, mostly contributing to the soft X-rays; (c) Comptonization by a standard hot ($k{T}_{\mathrm{e}}\gtrsim 100$ keV) and optically thin ($\ddot{I}„<0.5$) 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 $R_{\mathrm{hot}}\lesssim R_{\mathrm{warm}}\lesssim 10$ R${}_{\mathrm{g}}$. 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$\ddot{I}ƒ$ significance) evidence of which is indeed found in the RGS spectrum.

20 pages, 12 figures. Accepted for publication MNRAS