Left: A523 VLA 1.4 GHz image. Contour levels are drawn as in Fig. 1. Black dotted lines indicate the integration area for the flux measurement. Discrete sources embedded in the diffuse emission are alphabetically labeled, see Table 3. Right: A523 X-ray emission from in orange. The original image from the ROSAT All Sky Survey was convolved with a 225″ FWHM Gaussian. Solid contours are from the VLA 1425 MHz image and drawn at levels of  [1,2,4,8,...]  × 4σ_rms. Dashed contours show the galaxy iso-density distribution derived from INT images. Contours are drawn at  [1.0,1.2,1.4,...]  × 1.6 galaxies arcmin^-2 selecting only galaxies with colors 1.12 < V − R < 1.42, 0.25 < R − I < 0.55, i.e., within 0.15 magnitudes the V − R and R − I color of the central cD galaxy.