An explanation for the soft X-ray excess in active galactic nuclei

We present a large sample of type 1 active galactic nuclei (AGN) spectra taken with XMM-Newton, and fit them with both the conventional model (a power law and blackbody) and the relativistically blurred photoionized disc reflection model of Ross & Fabian. We find that the disc reflection model is a better fit. The disc reflection model successfully reproduces the continuum shape, including the soft excess, of all the sources. The model also reproduces many features that would conventionally be interpreted as absorption edges. We are able to use the model to infer the properties of the sources, specifically that the majority of black holes in the sample are strongly rotating, and that there is a deficit in sources with an inclination > 70 degrees. We conclude that the disc reflection model is an important tool in the study of AGN X-ray spectra.