Posterior distributions for the MCMC run with synthetic data for models A and B. The top panels of the triangles show the marginalized parameter posteriors (in arbitrary units); here the dark and light orange shadings give the 68% and 95% credible regions. The lower panels show the projected two-dimensional parameter posteriors against each other. For these panels the solid line encloses the 95% credible regions. The blue stripes show the original values of the synthetic data that were used to create the data: R = 12 km, M = 1.5 M_⊙, X = 0, and D = 6 kpc. If the composition is known, the radius is precisely recovered. When X is a free parameter, the prior limit of X > 0 and the correlation of M, X, and D with each other leads to asymmetric posteriors around the true value, and so the inferred radius is a lower limit.