2020MNRAS.493.1261N

This paper presents the first detection of Shapiro delay from the binary millisecond pulsar PSR J1811-2405. We report a 11σ measurement of the orthometric amplitude, h3 = 6.8(6) x 10-7, and a 16σ measurement of the orthometric ratio, s = 0.81(5). Given the relatively high orbital inclination, i = 79(2)°, of this binary system, we obtain constraints on the companion mass of mc=0.31^+0.08_–0.06 M_☉. The pulsar mass is currently less well constrained, with a value of 2.0^+0.8_–0.5 M_☉. The companion mass and the orbital period are in agreement with the prediction made by previous numerical calculations of the evolution of compact binary systems. From a study of the polarization, we find that the orbital inclination angle is ∼100° and that PSR J1811-2405 is an orthogonal rotator. In addition, the µs-level timing precision together with its narrow profile makes PSR J1811-2405 a good candidate for inclusion in the pulsar timing arrays being used to detect nHz gravitational waves.