Constraints on the NS mass and the orbital inclination angle of M3B, M3D and M3F, from left to right, assuming a flat prior for the inclination angle and a bimodal Gaussian prior for the NS mass, following Antoniadis et al. (2016). The one-dimensional histograms represent the marginalized probability distributions for these two parameters, with the solid blue and dashed black lines indicating the best-fit values and their associated uncertainties. The bottom-left panel shows the joint two-dimensional posterior probability distribution, with contours representing the 1σ, 2σ, and 3σ confidence levels. For M3D and M3F, the posterior distributions shown in cyan for the young solution and magenta for the old solution. The derived values for the companion mass, cooling age, effective temperature, NS mass and orbital inclination for the two solutions are listed in Table A.1.