Left: I_R − I_X relation of the halo in Abell 2744, extracted in square boxes with width of 10″ (about 45 kpc). The X-ray surface brightness is extracted from the Chandra (0.5−2.0 keV band) image smoothed with a Gaussian FWHM of 3″. The radio surface brightness is extracted from radio maps at 10″ resolution. The Linmix best-fit relations are indicated by red dashed lines. Green circles depict cells where the radio and X-ray surface brightness is above 3σ level. The upper limits (arrows) represent cells with data points below 2σ radio noise level. The horizontal black dash-dotted lines indicate the 1σ in the radio maps. Yellow show samples from the posterior distribution. The best-fit are reported with the corresponding 95% confidence regions. Lower panel: residuals of log I_R and log I_X with respect to the Linmix best fit line. The radio brightness strongly correlates with the X-ray at all three frequencies. The best-fitting slopes at 675 MHz, 1.5 GHz and 3 GHz are 0.73 ± 0.02, 0.75 ± 0.02, and 0.74 ± 0.02, respectively.