2026ApJ...999..115C

We present 15 yr of Nançay and Green Bank radio telescope timing observations for PSR J1231-1411. This millisecond pulsar is a primary science target for the Neutron Star Interior Composition Explorer telescope (NICER, which discovered its X-ray pulsations), has accumulated near-continuous γ-ray data since the Fermi-Large Area Telescope's launch, and has been studied extensively with the Green Bank and Nançay radio telescopes. We have undertaken a campaign with the Green Bank Telescope targeting specific orbital phases designed to improve our constraint on the pulsar's mass through the detection of a relativistic Shapiro delay. Both frequentist and Bayesian techniques-the latter incorporating priors from white dwarf binary evolution models-are applied to 15 yr of radio observations, yielding relatively weak constraints on the companion and pulsar masses of $0.2{3}_{-0.06}^{+0.09}$M_⊙ and $1.8{7}_{-0.67}^{+1.11}$M_⊙, respectively (68.3% CI from Bayesian fits); however, the orbital inclination is measured to better relative precision ($79.8{0}_{-4.70}^{+3.47}$°). Restricting the maximum allowed pulsar mass to 3 M_⊙ improves the constraint and lowers the measured mass to $1.7{1}_{-0.56}^{+0.70}$M_⊙. A fully generalized Bayesian fit that simultaneously samples the noise and timing models yields a pulsar mass in close agreement with this value. While our radio-derived inclination result has informed recent NICER X-ray studies of J1231-1411, the lessons learned from this troublesome pulsar will also bolster future high-precision mass measurement campaigns and resulting constraints on the neutron star interior equation of state.