Spatial correlation between X-ray and radio surface brightness. Left panel: I_R − I_X relation of the halo in A1413, extracted in square boxes with width of 35″. The horizontal gray dash-dotted lines indicate the σ_rms = 298 μJy beam⁻¹ in the radio maps. Right panel: I_R − I_X relation of the mini halo in A1413, extracted in square boxes with a width of 23″. The horizontal gray dash-dotted lines indicate the σ_rms = 203 μJy beam⁻¹ in the radio maps. For both relations, upper limits (cyan points) refer to cells where the radio surface brightness is below the 2σ_rms level. The best-fit (green dashed line) is reported with the corresponding 1σ confidence interval. Red dashed best-fit line (left panel) refers to the correlation without the four central boxes.