Though many sources show optically thin synchrotron spectra which appear power law in most of the radio band, with a unique spectral index, this is at best the approximation and there will be deviation which provide information about the source. The power law spectrum of the synchrotron electron typically will have a high and low energy cutoff which translates to a high and low frequency deviation from the power law spectrum. Figure 5.3 shows the schematic of an ideal power spectrum and one with cutoffs at 10 MHz and 1000 MHz. The deviation are often outside the observable radio band, but if detected can put constraints on the energetics of the source.
