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We report the discovery of seven new fossil systems in the 400d clustersurvey. Our search targets nearby, $z\le0.2$, and X-ray bright, $L_X\ge10^{43}$ erg sec$^{-1}$, clusters of galaxies. Where available, we measure theoptical luminosities from Sloan Digital Sky Survey images, thereby obtaininguniform sets of both X-ray and optical data. Our selection criteria identify 12fossil systems, out of which five are known from previous studies. While ingeneral agreement with earlier results, our larger sample size allows us to puttighter constraints on the number density of fossil clusters. It has beenpreviously reported that fossil groups are more X-ray bright than other X-raygroups of galaxies for the same optical luminosity. We find, however, that theX-ray brightness of massive fossil systems is consistent with that of thegeneral population of galaxy clusters and follows the same $L_X-L_{\rm opt}$scaling relation.

Fossil Systems in the 400d Cluster Catalog