The origin of the diffuse X-ray background

The Einstein Deep Survey fields are used to reexamine the problem of the origin of the extragalactic diffuse X-ray background. An approach based on fluctuation analysis is adopted, and a sophisticated Monte Carlo scheme is used to compare the X-ray images with a variety of models representing point and diffuse source contributions. Results are presented for two classes of models: those which determine the flux cutoff beyond which pointlike sources fail to contribute significantly if the log N-log S slope is fixed at the measured value of -1.5, and those which set limits on the slope of the log N-log S relation below its last measured point at the Deep Survey threshold. In both cases, it is found that the known population of X-ray-emitting quasars and any reasonable extrapolations therefrom do not comprise the entire X-ray background.