X-ray properties of quasars and results from a deep X-ray survey of optically selected objects

A sample of 178 optically selected quasars and Seyfert galaxies is studied. Seventy seven of the objects have measured X-ray fluxes while the remainder have upper limits. The analysis strengthens and confirms the conclusion of Avni and Tananbaum (1982) that the X-ray-to-optical luminosity ratio of optically selected quasars decreases with increasing optical luminosity. The dependence of the ratio on look-back time is small and may be null. This suggests that the effect is intrinsic to the physical processes that give rise to the nonthermal emission in quasars. 43 references