Modelling of radio spectra obtained by VLA on ∆t = 201 and 221 days after optical discovery. The left panel shows the fitting of Eq. (5) to the spectra, assuming SSA as the only absorption mechanism. The right panel shows the fitting of Eq. (5) multiplied by Eq. (6) to the spectra, assuming that the absorption is due to both SSA and FFA by the material in front of the shock. Both fits also show shaded lines uniformly drawn from the posteriors of the fitted parameters.