The FAST Galactic Plane Pulsar Snapshot Survey. Ⅶ. Six Millisecond Pulsars in Compact Orbits with Massive White Dwarf Companions

Binary millisecond pulsars with a massive white dwarf （WD） companion are intermediate-mass binary pulsar（IMBPs）.They are formed via the Case BB Roche-lobe overflow evolution channel if they are in compact orbit with an orbital period of less than 1 day.They are fairly rare in the known pulsar population;only five such IMBP have been discovered before,and one of them is in a globular cluster.Here we report six IMBPs in compact orbits PSRs J0416+5201,J0520+3722,J1919+1341,J1943+2210,J1947+2304 and J2023+2853,discovered during the Galactic Plane Pulsar Snapshot survey by using the Five-hundred-meter Aperture Spherical radio Telescope doubling the number of such IMBPs due to the high survey sensitivity in the short survey time of 5 minutes Follow-up timing observations show that they all have either a CO WD or an ONeMg WD companion with a mas greater than about 0.8 M⊙in a very circular orbit with an eccentricity in the order of?10-5.PSR J0416+5201should be an ONeMg WD companion with a remarkable minimum mass of 1.28 M⊙.These massive WD companions lead to a detectable Shapiro delay for PSRs J0416+5201,J0520+3722,J1943+2210,and J2023+2853,indicating that their orbits are highly inclined.From the measurement of the Shapiro delay,the pulsar mas of J1943+2210 was constrained to be 1.84-0.09+0.11M⊙,and that of PSR J2023+2853 to be 1.28-0.05+0.06M⊙.