Probing Cluster Potentials through Gravitational Lensing of Background X-Ray Sources

We examine the gravitational lensing effect of a foreground galaxy cluster on the number count statistics of background X-ray sources. The lensing produces a deficit in the number of resolved sources in a ring close to the critical radius of the cluster. This deficit could be detected at the $\sim 3\sigma$ level with the AXAF-ACIS camera.