Bridge emission profile after masking of unrelated sources. Upper panel: compact source-subtracted image (see Sect. 4 and Fig. 6) with non-bridge sources masked out (white ellipses). A white line grid is used to measure the bridge brightness profile. The grid is tilted by 25° and has the same reference point (centre) as Govoni et al. (2019). The lines are separated by 144 kpc (one beam width) and their length is 3 Mpc. Lower panel: surface brightness profile extracted by measuring the average surface brightness in each slice.