Follow-up Timing of 12 Pulsars Discovered in Commensal Radio Astronomy FAST Survey

We present phase-connected timing ephemerides, polarization pulse profiles, and Faraday rotation measurements of 12 pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the Commensal Radio Astronomy FAST Survey. The observational data for each pulsar span at least 1 yr. Among them, PSR J1840+2843 shows subpulse drifting, and five pulsars are detected to exhibit pulse nulling phenomena. PSR J0640‑0139 and PSR J2031‑1254 are isolated millisecond pulsars (MSPs) with stable spin-down rates ( Ṗ ) of 4.8981(6) × 10^‑20 s s^‑1 and 6.01(2) × 10^‑21 s s^‑1, respectively. Additionally, one pulsar (PSR J1602‑0611) is in a neutron star‑white dwarf (WD) binary system with an 18.23-day orbit and a companion of ≤0.65 M _⊙. PSR J1602‑0611 has a spin period, companion mass, and orbital eccentricity that are consistent with the theoretical expectations for MSP‑helium WD (He WD) systems. Therefore, we believe that it might be an MSP‑He WD binary system. The locations of PSR J1751‑0542 and PSR J1840+2843 on the P‑Ṗ diagram are beyond the traditional death line. This indicates that FAST has discovered some low- Ė pulsars, contributing new samples for testing pulsar radiation theories. We estimated the distances of these 12 pulsars based on NE2001 and YMW16 electron density models, and our work enhances the data set for investigating the electron density model of the Galaxy.