ChaMP and the High Redshift Quasars in X-rays
  Chandra X-ray Observatory, (formerly known as AXAF), will observe down to the flux limit of 2\times 10^{-16} erg~s^{-1} cm^{-2}. In its first year of operation Chandra's CCD detectors will observe over 1500 quasars serendipitously in the soft (0.5--3.5 keV) band. Over 200 quasars will be detected in X-rays in the redshift range 3<z<4 and over 400 quasars in 2<z<3. This will enable us to determine the high redshift X-ray luminosity function. This is the contribution by unabsorbed sources only. The total numbers would be larger by about 60% 
S. Mathur (OSU, CfA), H. Marshall (MIT), N. Evans, P. Green, B. Wilkes   (CfA)