Mass Measurements of the Double Neutron Star System PSR J0641+0448

Pulsar timing of double neutron star (DNS) systems is one of the best methodologies to study the neutron star mass distribution. Here we report the discovery of a DNS system PSR J0641+0448 in the Five-hundred-meter Aperture Spherical radio Telescope (FAST) Galactic Plane Pulsar Snapshot survey. This pulsar has a 25.7 ms spin period and moves in a 3.73 day eccentric orbit with an eccentricity of 0.145. Using FAST observations, we obtained its phase-connected timing solution with periastron advance and Shapiro delay detected. Using χ 2 analysis based on the DDGR model, we constrain the pulsar mass to 1.31 9 − 0.035 + 0.021 M ⊙ , and the companion mass to 1.26 9 − 0.016 + 0.022 M ⊙ with a 68.3% confidence level. The low companion mass and mild orbital eccentricity are consistent with the correlation between neutron masses and orbital eccentricities.