2026ApJ..1000L...1Y

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 χ² analysis based on the DDGR model, we constrain the pulsar mass to $1.31{9}_{-0.035}^{+0.021}\,{M}_{\odot }$, and the companion mass to $1.26{9}_{-0.016}^{+0.022}\,{M}_{\odot }$ 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.