The solid line shows the ratio between the power-law fit to the cocoon zone (Fig. 10) and the CI-model fit to the flow zones (Fig. 11(c)). The dashed line shows the ratio between the CI-model fits to the flow zones (Fig. 11(c)) and to the halo (Fig. 11(b)). Simple synchrotron ageing would have left untouched the low-frequency part of the spectrum, producing in this plot a horizontal line until the point where the break frequency occurs. We notice instead a steepening in the spectrum, going from the central region to the flows and, to a lesser extent, from the flows to the halo.