(a): prior and posterior distributions for the waveguide density in the inversion of Eq. (9) with v_ph = 1030 ± 410 km s⁻¹, under model M₁. (b): comparison between the marginal posteriors for magnetic field strength in the same inversion for the cases of uniform and Gaussian prior on the waveguide density. (c) and (d): comparison between the joint two-dimensional posterior distributions for the internal density of the waveguide and the magnetic field strength obtained for the inference with v_ph = 1030 ± 410 km s⁻¹, under model M₁, for the cases of uniform priors (c) and a Gaussian prior for the internal density with μ_ρi = 1.9 × 10⁻¹² kg m⁻³ and σ_ρi = 0.5μ_ρi (d). The inference with the more informative prior on density leads to G and kg m⁻³. Bottom panels: the outer boundaries of the light grey and dark grey shaded regions indicate the 95% and 68% credible regions.