M ULMER (a), C ADAMI (a), R PILDIS (a), A ROMER (b), R NICHOL (b), B HOLDEN (c), R KRON (c)
(a) Dept. of Physics and Astronomy, Northwestern University Evanston, IL 60208-2900, USA
(b) Dept. of Physics, Carnegie Mellon University Pittsburgh, PA 15213 (c) Dept. of Astronomy \& Astrophysics, University of Chicago, Chicago, IL 60637

We summarize the results of the Bright SHARC (Serendipitous High-redshift Archival ROSAT Cluster) survey ( This is a search for distant X-ray bright clusters, which must be corrected for completeness in order to convert these results into a luminosity function. We have completed a thorough simulation of the SHARC survey. We show that our new improved results have produced no major change to the results of the recently published paper of Nichol {\em et al.} on cluster luminosity evolution. Besides statistics, the uncertainty in the luminosity function derived from X-ray surveys is large, because we do not know the distribution of X-ray cluster morphologies at high redshift. Our simulations show that to fully understand the completeness of deep surveys, the distribution of the shapes of the clusters must be understood. For, sharply peaked or highly elliptical clusters are the easiest to detect. Beyond the Bright SHARC, we have initiated a search for more distant X-ray luminous clusters. We have found preliminary evidence for the detection of up to four high-redshift X-ray luminous cluster.