A Shapiro Delay Detection in the Binary System Hosting the Millisecond Pulsar PSR J1910–5959A

PSR J1910-5959A is a binary pulsar with a helium white dwarf (HeWD) companion located about 6 arc min from the center of the globular cluster NGC 6752. Based on 12 years of observations at the Parkes radio telescope, the relativistic Shapiro delay has been detected in this system. We obtain a companion mass M-C = 0.180 +/- 0.018 M-circle dot (1 sigma) implying that the pulsar mass lies in the range 1.1 M-circle dot <= M-P <= 1.5 M-circle dot. We compare our results with previous optical determinations of the companion mass and examine prospects for using this new measurement for calibrating the mass-radius relation for HeWDs and for investigating their evolution in a pulsar binary system. Finally, we examine the set of binary systems hosting a millisecond pulsar and a low-mass HeWD for which the mass of both stars has been measured. We confirm that the correlation between the companion mass and the orbital period predicted by Tauris & Savonije reproduces the observed values but find that the predicted M-P-P-B correlation overestimates the neutron star mass by about 0.5 M-circle dot in the orbital period range covered by the observations. Moreover, a few systems do not obey the observed M-P-P-B correlation. We discuss these results in the framework of the mechanisms that inhibit the accretion of matter by a neutron star during its evolution in a low-mass X-ray binary.