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We examine the surface density of quasars expected in the ROSAT PSPC surveys, using quasar optical luminosity functions and model continuum spectra including a soft X-ray excess. We show that the surface density is a sensitive function of the characteristic energy of the soft excess, and the absorption within the quasar as well as the interstellar medium. Comparision of the predicted surface density with the results of various surveys allows useful constraints to be put on the nature of the soft excess.
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