Overdensity of X-ray Sources in the Field of Nearby Clusters of Galaxies
  Two nearby clusters of galaxies: A194 (z=0.018) and A1060 (z=0.0114) have been analyzed for their X-ray point source properties with XMM-Newton EPIC-PN data. A multi-band source detection technique was applied to both of the clusters, resulting in 46 sources from the A194 field and 32 sources from the A1060 field, respectively. The cumulative log(N)-log(S) for a flux limit of Fx~10E-14 ergs cm-2 s-1 is calculated and compared with that of the Lockman Hole. A ~3 sigma excess of X-ray sources is found for the cluster regions. Considering the higher fraction observed in optical studies from the clusters, we estimate that the cluster source density is 6 times higher than the blank field source density, and 15 times higher than the local group. Our X-ray selected sources have luminosity values between 10E(39.6)<Lx<10E(41.4) ergs/s, in which X-ray emission from LMXBs, hot halos and starburst galaxies becomes noticeable. The significance of the source density excess vanishes gradually for sources with Lx > 10E(40.5) ergs/s, at which point the source density becomes comparable to that of the blank-field level. Considering this confined low luminosity range and the X-ray to optical luminosity ratios (L_X/L_B), the observed overdensity is ascribed to AGN fueling by its infall into cluster environment for Lx < 10E(40.5) ergs/s in the X-ray luminosity function. Whereas, the quenching of AGN activity by the deep cluster potential explains why the excess of the source density vanishes for the brighter sources. 
Murat Hudaverdi, Hideyo Kunieda, Takeshi Tanaka, Yoshito Haba, Akihiro   Furuzawa, Yuzuru Tawara and E. Nihal Ercan