68′ × 68′ combined (MOS1+MOS2+pn) tile smoothed with MR/1 on which preliminary source detection with SEXtractor has been run. The figure is the smoothed version of the left panel of Fig. 2. Green circles indicate sources tentatively identified by SEXtractor. Detected sources include clusters (larger sources regularly spaced by 10′) with count rates of 0.1 count s^-1 and core radius 20′′, and resolved AGNs inserted at random positions (smaller sources irregularly spaced). The exposure time is 10 ks and background is added. Cyan circles represent the XMM pointings and are 15′ in radius; the pointing geometrical centres at which the circles are drawn are not the same as the centres of the optics (points of maximum telescope sensitivity).