Are there X-ray quiet quasars

GTThe Xraytooptical energy distribution of quasars, alpha_ox, is requiredto relate the quasar statistics, evolution and luminosity function in the twowavebands and to understand its. broad band emission. In a recent study ofradioquiet quasars from ROSAT observations there is a small number of objectsshowing very weak Xray emission compared to their optical luminosity. Thenature of these Xray quiet quasars is unknown and it is not clear whether theyare the Xray quiet extremes of a continous distribution or a distinct class ofobjects. XMM observations seem to be the only way to understand this newpopulation of quasars and to distinguish different explanations for the unknownphysical nature of these objects. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]