The soft x-ray excess in quasars

Abstract

A soft x-ray excess in the energy range of a few tenths of a ke V has been detected in some quasars , and there are indications in the x-ray data which point to the excess being a feature universal to all quasars. The poor energy resolution in the concerned energy band make it impossible at the present to observationally constrain the excess quantitatively. We show in this paper that the shape of the excess sensitively determines the surface density therefore allows an assessment of the nature of the excess