2024ApJ...966...26T

We performed near-daily observations of the binary pulsars PSR J0218+4232, PSR J1518+4904, and PSR J2023+2853 with the Canadian Hydrogen Intensity Mapping Experiment (CHIME). For the first time, we detected the Shapiro time delay in all three pulsar binary systems, using only 2-4 yr of CHIME/Pulsar timing data. We measured the pulsar masses to be ${1.49}_{-0.20}^{+0.23}$M_⊙, ${1.470}_{-0.034}^{+0.030}$M_⊙, and ${1.50}_{-0.38}^{+0.49}$M_⊙, respectively. The companion mass to PSR J0218+4232 was found to be ${0.179}_{-0.016}^{+0.018}$M_⊙. We constrained the mass of the neutron star companion of PSR J1518+4904 to be ${1.248}_{-0.029}^{+0.035}$M_⊙, using the observed apsidal motion as a constraint on the mass estimation. The binary companion to PSR J2023+2853 was found to have a mass of ${0.93}_{-0.14}^{+0.17}$M_⊙; in the context of the near-circular orbit, this mass estimate suggests that the companion to PSR J2023+2853 is likely a high-mass white dwarf. By comparing the timing model obtained for PSR J0218+4232 with previous observations, we found a significant change in the observed orbital period of the system of $\dot{{P}_{{\rm{b}}}}=0.14(2)\times {10}^{-12}$; we determined that this variation arises from “Shklovskii acceleration” due to the relative motion of the binary system, and used this measurement to estimate a distance of d = (6.7 ± 1.0) kpc to PSR J0218+4232. This work demonstrates the capability of high-cadence observations, enabled by the CHIME/Pulsar system, to detect and refine general-relativistic effects of binary pulsars over short observing timescales.