Selection of SXCS cluster candidates imaged by the Sloan Digital Sky Survey (SDSS) with X-ray contours overlaid in green. The image size is 3  ×  3 arcmin. The X-ray contours are computed on XRT images in the 0.5−2 keV energy band with the Chandra Ciao software, and the contours are drawn at respectively 9, 15, 30, 50, 90, 160 and 300σ, where σ is given by the local background level.