The spectral energy distribution of the Seyfert galaxy Ton S180

We present spectral results from a multisatellite, broadband campaign on the narrow-line Seyfert 1 galaxy Ton S180 ( PHL 912) performed at the end of 1999. We discuss the spectral energy distribution ( SED) of the source, combining simultaneous Chandra, ASCA, and Extreme Ultraviolet Explorer data with contemporaneous Far Ultraviolet Spectroscopic Explorer ( FUSE), Hubble Space Telescope, and ground-based optical and infrared data. The resulting SED shows that most of the energy is emitted in the 10-100 eV regime, which must be dominated by the primary energy source. No spectral turnover is evident in the UV regime. This, the strong soft X-ray emission, and the overall shape of the SED indicate that emission from the accretion disk peaks between 15 and 100 eV. High-resolution FUSE spectra showing UV absorption due to O vi and the lack of detectable X-ray absorption in the Chandra spectrum demonstrate the presence of a low column density of highly ionized gas along our line of sight. The highly ionized state of the circumnuclear gas is most likely linked to the high luminosity and steep spectrum of the active nucleus. Given the strong ionizing flux in Ton S180, it is possible that the clouds within a few tens of light days of the central source are too highly ionized to produce much line emission. Thus, the narrow width of the emission lines in Ton S180 is due to the emission arising from large radii.