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   PR # 21120
     We propose the high z QSO which were detected by the all sky survey 
    of ROSAT. This proposal has selected brighter radio loud QSO among   
    these QSO. Therefore, it is expected that the observation time 20 or 
    40 ksec is enough to investigate the spectral structure of these QSO.
    The z dependence of spectral index is expected from a Compton reflect
    ion model of X-ray spectrum. It is very important for CXB to know the
    spectral structure of QSO with z=2 - 4 in terms of a scheme of AGN   
    origin of CXB.                                                       
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