Left: the P_{1.4   GHz} − L_X plane for mini-halos. The black arrows are the upper limits on the detection of mini-halos (see Sect. 5.1). The black filled circles are mini-halos detected in the GRHS sample. Red points are other mini-halos from the literature (Feretti et al. 2012). The black, solid straight line is the best fit obtained for a possible scaling between the radio-power and X-ray luminosity using only detected mini-halos. The black curved lines encompass the 95% confidence region (i.e. the region that has a 95% probability of containing the regression line). The dashed line is a best fit also including the upper limits. Right: the distribution of the same mini-halos and upper limits in the radio versus X-ray flux plane. The solid line has a slope 0.77 ± 0.17, and the dashed line has a slope 1.17 ± 0.25.