Preliminary constraints on the outer orbital parameters. Panel (A): residual distribution of the FAST-measured pulsar periods (δP in milliseconds) versus eccentricity e₂ and orbital frequency f_orb2 (yr⁻¹), plotted on a logarithmic scale. The best fits follow the darker curve, which shows the coupling between e₂ and f_orb2. Panel (B): best-fit δP as a function of f_orb2 for a given set of M_star = 1 M_⊙ and S_⊥ = 11,000 lt-s constrained from the optical and infrared counterpart. The total mass M_t for the optimal orbital parameters should be in the range 2.4–3.6 M_⊙, with f_orb2 highlighted by the shaded region, corresponding to the orbital period of the outer orbit P_orb2 between 50 and 150 yr and the eccentricity e₂ between 0.50 and 0.75.