Fluctuations in the X-ray Background

The fluctuations in the X-ray background at high galactic latitudes give an upper limit to the counts of extragalactic X-ray sources near the intensity level corresponding to one source per beam width. The general mathematical relation between the source counts and the probability distribution of the resulting contribution to the fluctuations is known, and is here computed for various extrapolations of the observed source counts to fainter sources. The observed limits to background fluctuations are consistent with a uniform distribution of sources in space.