Differential photon energy densities at their characteristic frequencies. The data points for knot C and NE refer to the internal background photon energy densities according to Gallimore et al. (2004) (at 5 GHz) and the ones for P1-P4 refer to the data from Michiyama et al. (2022) (at 92 GHz). For the conversion of the radio data of the six knots knot radii of r_k, 1 = 0.2 ± 0.1 pc, r_k, 2 = 0.3 ± 0.15 pc and r_k, 3 = 3.5 ± 1.75 pc, respectively, are assumed.