Standard deviation of the δS_ν distribution normalized by that at 150 MHz at the shock-front at 184.7 Myr for all our models at all frequencies. The top, middle and bottom rows correspond to the fresh injection model, the re-acceleration model assuming a Dirac Delta pre-existing distribution function and the re-acceleration model assuming a power-law pre-existing distribution function, respectively. The first and third columns show the results from the original maps and the second and fourth columns show the results of the map smoothed with 5″ × 5″ (dot-dashed) and 20″ × 20″ (dashed) beam sizes.