ROSAT observations of z>3 quasars

Successful pointed observations using the ROSAT PSPC were made of seven z>3 optically selected quasars from the Large Bright Quasar Survey (LBQS). Four detections and three 3σ upper limits resulted. Combining these data with the heterogeneous sample of Avni & Tananbaum [ApJ, 305, 83 (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_BJ < 18.85; the result is about 5%.