The origin of the soft excess in high L/L_Edd AGN

Abstract

We discuss the origin of the soft X-ray excess seen in AGN. There are clear advantages to models where this arises from atomic processes in partially ionised material rather than where it is a true continuum component. However, current data cannot distinguish between models where this material is seen in reflection or absorption, even for the archetypal 'reflection dominated' AGN MCG-6-30-15. Instead, we give physical arguments on the ionisation structure of X-ray illuminated material which exclude a reflection origin if the disc is in hydrostatic equilibrium. The same physical processes strongly favour an absorption origin for the soft excess, giving a more messy picture of the accretion environment. This implies that these apparently 'reflection dominated' AGN are not good places to test GR, but they do give insight into the spectra expected from the first QSO's in the early Universe.