Evolution of the ROSAT AGN Luminosity Function
  We present the results and parameterization of the 0.5-2 keV Luminosity Function of AGNs from various ROSAT Surveys, ranging from the ROSAT bright Survey from the ROSAT All-Sky Survey (RASS) to the Ultra-Deep survey on the Lockman hole. A Luminosity-dependent density evolution model, where the density evolution rate drops at low luminosities, gives an excellent parametric description of the overall XLF covering wide ranges of redshift and luminosity.   The number density evolution of high-luminosity AGNs in our sample shows a similar behavior to optical and radio surveys, except that we do not find evidence for the rapid decrease of the number density at z>2.7. The discrepancy is marginally significant and including more deep survey results would make better determination of the behavior. 
T. Miyaji, G. Hasinger, M. Schmidt