Abstract
With the superb angular resolution of the Chandra Observatory, it is now
possible to detect X-ray point sources, either embedded in galaxy clusters or
along the cluster line of sight, which could not be resolved by previous
instruments. This now allows studies of source counts in distant cluster
fields. A sample of 18 distant (0.25 < z < 1.01) galaxy clusters from the
Chandra archive were used to analyze the inner region of clusters of galaxies
to check for the presence of any overdensity of X-ray point sources embedded in
the gas diffuse emission. We constructed the logN-logS, in both the soft and
hard energy bands, for the X-ray point sources detected in the central cluster
region (within 1 Mpc)to be compared with the counts of point sources detected
in similarly deep fields without clusters. We find a ~ 2 sigma excess of
cluster region sources at the bright end of the logN-logS. The radial
distribution of the brightest X-ray point sources confirms this excess and
indicates that it is confined to the inner 0.5 Mpc of the cluster region. The
results suggest the possible existence of X-ray sources belonging to the
cluster (most probably AGN, given their 0.5-10 keV luminosity ranging from
10^43 to 10^44 erg/s): on average one every three clusters. The X-ray source
excess found here is much smaller than the excess of radio galaxies found
recently in high-z X-ray selected clusters, possibly due to the higher
sensitivity of the radio observations.
