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   63029
   Recent ROSAT and ASCA observations of several high-redshift radio-loud
   quasars have unambiguosly revelead that substantial intrinsic
   absorption, evolving with the cosmic time, is a common property among
   these objects. On the other side, the spectral evolutive properties of
   radio-quiet quasars are poorly known due to the paucity of the observed
   objects. In a collaborative effort with our Japanese colleagues at
   RIKEN we have undertaken a project aimed to build a sizeable sample of
   high-redshift radio-quiet quasars (RQQ). The here proposed observations
   of two z > 2 RQQ will allow us to obtain broad band X--ray spectra of
   good statistical quality. The comparison with the already available
   data will permit to study with unprecedent detail the quasar emission
   mechanism and its evolution.
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