SDSS g-band image of the galaxy cluster A1213 with, superimposed, the contour levels of the VLA 1.4 GHz radio image by G09 (red thick contours, HPBW = 35″ × 35″, first contour level at 1 mJy beam⁻¹, the others spaced by a factor ). Thin blue contours show the (smoothed) X-ray emission of the cluster as derived from the XMM-Newton archival image ID 0550270101 (photons in the energy range 0.7−1.2 keV). Labels denote galaxies discussed in the text. The arrow highlights the diffuse radio emission classified by G09 as a small-size radio halo. The black cross shows the position of the centroid of the X-ray emission (see Sect. 6).