Einstein observations of quasars

X-ray observations of quasars with the imaging proportional counter and the high-resolution imager aboard the Einstein X-ray Observatory are reviewed. Detailed results are discussed for seven quasars with redshifts of 0.07 to 3.1. Data on 40 X-ray quasars observed with the Einstein imaging systems are summarized in the form of plots of 0.5-4.5-keV X-ray luminosity vs. redshift and of K-corrected X-ray emission vs. K-corrected optical flux. The results show that: (1) quasars as a class are luminous X-ray emitters; (2) quasars are a major contributor to the 2-keV X-ray background; (3) X-ray observations of quasars can be combined with observations of the X-ray background to set limits on the number of faint quasars; and (4) the Einstein imaging systems could detect quasars with redshifts of 3 to 10.