An explanation for the soft X-ray excess in AGN (Conference proceedings version)

Abstract

We present a large sample of type 1 AGN spectra taken with XMM-Newton. We fit them with the relativistically blurred photoionized disc model of Ross & Fabian (2005). This model is based on an illuminated accretion disc of fluorescing and Compton-scattering gas, and includes relativistic Doppler effects due to the rapid motion of the disc and general relativistic effects such as gravitational redshift due to presence of the black hole. The disc model successfully reproduces the X-ray continuum shape, including the soft excess, of all the sources. It provides a natural explanation for the observation that the soft excess is at a constant temperature over a wide range of AGN properties. The model also reproduces many features that would conventionally be interpreted as absorption edges. We use the model to measure properties of the AGN such as inclination, black hole rotation, and metallicity.