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Published online by Cambridge University Press: 19 July 2016
We found that ROSAT spectra of a sample of 89 AGN are generally steeper than 0.7. The excess above a hard X-ray power law spectrum in this energy range which has been found already with Einstein and EXOSAT for some AGN is now seen very clearly in most sources. Our α-disk models (Dörrer et al., 1992 and references therein) which include Comptonization and relativistic corrections are in agreement with the measured soft excesses when the (ṀEdd. , α) parameter space is restricted to α > 0.4 and ṀEdd. ε [0.4, 0.8] (ṀEdd. : Eddington accretion rate).