Bayesian two-dimensional analysis of the RM structure function S(Δr) and depolarization ratio FPOL/FPOL₀(λ⁴). Top right panel: image of the posterior distribution of the model parameters along with one-dimensional marginalizations. Top left panel: dots represent the observed S(Δr) (error bars are comparable to the size of the symbols). The fan plot represents the population of synthetic RM structure functions from the posterior distribution. Bottom left panel: depolarization ratio as a function of λ⁴ for the southern lobe of 3C 40B. The dots represent the observed data while the fan plot represents the population of synthetic depolarization ratio extracted from the posterior distribution of model parameters. Bottom right panel: depolarization ratio as a function of λ⁴ for the northern lobe of 3C 40B.