ROSAT OBSERVATIONS OF Z-GREATER-THAN-3 QUASARS

Successful pointed observations using the ROSAT PSPC were made of seve n z>3 optically selected quasars from the Large Bright Quasar Survey ( LBQS). Four detections and three 3 sigma upper limits resulted. Combin ing these data with the heterogeneous sample of Avni and Tananbaum [Ap J, 305, 83 (1986)] confirms their conclusion that the ratio of x-ray t o optical luminosity is correlated with optical luminosity and probabl y not correlated with redshift. This suggests that x-ray luminosity ev olves more slowly than optical luminosity. These results are then used in conjunction with the LBQS database to estimate the contribution to the 2 keV x-ray background of bright, optically selected quasars with m(BJ) < 18.85; the result is about 5%.