Spectral index maps of the inner and outer double of J1528+0544, presented as color maps. The color bars represent the scales given next to each panel. The gray line marks the inferred jet axes, along which a slice through the image was made to create spectral index profile shown in Fig. 7. Top left: spectral index map of the whole radio galaxy. A 700 MHz contour map is overlaid for reference. The contour levels are (3, 9, 39, 165)×0.33 mJy/b.a. The size of the circular beam for the color and contour maps is 45″. The traces of emission with low spectral index value are marked with a red polygon. Top right: spectral index map of the inner double without the diffuse relic emission. A tapered 4500 MHz contour map is overlaid for reference. The contour levels are (3, 9, 39, 165)×0.03 mJy/b.a. The size of the circular beam for the color and contour maps is 3″. Bottom left: spectral index 1σ error map of the whole radio galaxy. The contour map is the same as in the top left panel. Bottom right: spectral index 1σ error map of the inner double. The contour map is the same as in the top right panel.