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 masses distribution. Here we report the discovery of a double neutron star system PSR J0641+0448 in the Five-hundred-meter Aperture Spherical radio Telescope (FAST) Galactic Plane Pulsar Snapshot (GPPS) survey. This pulsar has a 25.7 ms spin period and moves in a 3.73-days 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 ${\chi }^2$ analysis based on DDGR model, we constrain the pulsar mass to $1.319_{-0.035}^{+0.021}{M}_{\odot }$, and the companion mass to $1.269_{-0.016}^{+0.022}{M}_{\odot }$ with a 68.3% confidence level. The low companion mass and mild orbital eccentricity is consistent with the correlation between neutron masses and orbital eccentricities.