Spectral index maps between uGMRT Band 4 (robust=−2.0) and Band 5 (robust=0.0) of the radio galaxies in the three clusters in the A3528 cluster complex, namely J1254-2900 and J1254-2901a (top left panel), J1254-2901b (top centre panel), J1254-2904 (top right panel), J1254-2913 (bottom left panel), J1254-2916 (bottom centre panel), and J1257-3021 (bottom right panel). The resolutions of the maps are 4.5″ (A3528N), 3.9″ (A3528S), and 3.7″ (A3532). The corresponding uncertainty error maps are shown in Fig. C.2. The radio contours are drawn at 3σ_rms × [1, 2, 4, 8, 16, 32, …] of the uGMRT Band 5 observations at the same resolution (not primary beam corrected; see Table 3 for the noise level).