Left: monochromatic radio power of radio halos at 1.4 GHz versus the cluster X-ray luminosity in the 0.1–2.4 keV band. Right: monochromatic radio power of halos at 1.4 GHz versus their LLS measured at the same frequency. The data are taken from the recent compilation of Feretti et al. (2012) and references therein. Blue dots are classical radio halos while empty blue dots are outlier clusters. The new halos detected in this work are indicated with red triangles.