ROSAT observations of z greater than 3 quasars

Successful pointed observations using the Roentgen Satellite (ROSAT) Position Sensitive Proportional Counter (PSPC) were made of seven z greater than 3 optically selected quasars from the Large Bright Quasar Survey (LBQS). Four detections and three 3 sigma upper limits resulted. Combining these data with the heterogeneous sample of Avni & Tananbaum (1986) confirms their conclusion that the ratio of x-ray to optical luminosity is correlated with optical luminosity and probably not correlated with redshift. This suggests that x-ray luminosity evolves 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(sub B(sub J)) less than 18.85; the result is about 5%.