Spectral index map of selected epochs. The contour levels were set at −1%, 1%, 2%, 4%, 8%, 16%, 32%, and 64% of the intensity peak at each epoch. The total intensity cut-off was set at 50σ. The limiting values for the spectral indices are indicated in the colour bars beside each panel. A summary of the image parameters is presented in Table F.10. The corresponding spectral index uncertainty maps are presented in Fig. D.1.