a) Expansion of supernova SN 1993J. The radii were measured with the CPM applied to the images obtained from the process described in Sect. 2 (we call these sizes R_SC). The dashed line corresponds to the model given by Eq. (2), fitted to only the 1.7 GHz data. The continuous line is the model given by Eq. (1), fitted to the data at higher frequencies. b) Same as in a), but in logarithmic scale.