Binary Millisecond Pulsar Mass Measurements from the NANOGrav 15-year Data Set

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Physics Frontiers Center is a pulsar timing array experiment designed to detect low-frequency gravitational waves from supermassive black hole binary mergers. NANOGrav conducts monthly cadence, high-precision pulsar timing observations of 72 millisecond pulsars (MSPs), many of which have timing baselines of >10 years. While the upcoming NANOGrav 15-year data set will facilitate a remarkably sensitive search for gravitational waves, it will also serve as a rich collection of high precision (sub-microsecond) pulsar timing data. Using both Bayesian timing and least-squares gridding techniques, we present new and updated measurements of orbital inclination angles, companion masses, and pulsar masses (where available) as well as other orbital parameters for the 48 binary MSP sources included in the 15-year data set. Among these are J0740+6620 and J1614-2230 — two of the most massive neutron stars known — and other sources of interest for constraining the neutron star interior equation of state. Such a census of MSP binaries also aids significantly in characterizing the overall distribution of neutron star masses.