On the Mass and Inclination of the PSR J2019+2425 Binary System

We report on 9 years of timing observations of PSR J2019+2425, a millisecond pulsar in a wide 76.5 day orbit with a white dwarf. We measure a significant change over time of the projected semimajor axis of the orbit, / x = × 10 -15 s -1 , where x ≡ ( a 1 sin i )/ c . We attribute this to the proper motion of the binary. This constrains the inclination angle to i < 72 ° , with a median likelihood value of 63°. A similar limit on the inclination angle arises from the lack of a detectable Shapiro delay signal. These limits on inclination angle, combined with a model of the evolution of the system, imply that the neutron star mass is at most 1.51 M ☉ ; the median likelihood value is 1.33 M ☉ . In addition to these timing results, we present a polarization profile of this source. Fits of the linear polarization position angle to the rotating vector model indicate that the magnetic axis is close to alignment with the rotation axis, α < 30 ° .