2013ApJ...777....2L

The ultraviolet (UV) to X-ray continuum of active galactic nuclei (AGNs) is important for maintaining the ionization and thermal balance of the warm absorbers (WAs). However, the spectra in the sensitive energy range ∼13.6-300 eV are unobservable due to Galactic extinction. Moreover, many AGNs show soft X-ray excess emission of varying strength in the 0.1 - 2 keV band, whose origin is still highly debated. This soft excess connects to the UV bump in the unobserved region of 13.6-300 eV. Here, we investigate the effect of the assumed physical model for the soft excess on the flux of the unobserved part of the spectrum and its effect on the WA properties. We perform a case study using XMM-Newton observations of the bright Seyfert 1 galaxy IRAS 13349+2438 with WA features. Two different physical models for the soft excess (blurred Compton reflection from an ionized disk and optically thick thermal Comptonization of the disk photons) predict different fluxes in the unobserved energy range. However, the current X-ray data quality does not allow us to distinguish between them using derived WA parameters. This, in turn, implies that it is difficult to determine the origin of the soft excess emission using the WA features.