Radio, X-ray, and Compon parameter observations vs. simulations. Top row: observations of the galaxy cluster pair A399–A401, with radio contours at about 1.4 GHz over-imposed on the X-ray images in the band 0.2–12 keV in red colors (Murgia et al. 2010) on the left, and radio contours at about 150 MHz (Govoni et al. 2019) over-imposed on the Compton parameter images in yellow colors (Hincks et al. 2022) on the right. Middle row: same as top row, but produced from the simulations presented in this work, assuming equipartition between magnetic field and relativistic electrons at each point of the computational grid. Bottom row: same as top row, but produced from the simulations presented in this work, assuming a coupling between the relativistic and thermal electrons. In the left panels, contour levels start at 120 μJy/beam and increase by factors of two, with a spatial resolution of 45″. In the right panels, contour levels start at 3 mJy/beam and increase by factors of two, with a spatial resolution of 80″.