High-cadence Timing of Binary Pulsars with CHIME

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 circle dot, 1.470 - 0.034 + 0.030 M circle dot, and 1.50 - 0.38 + 0.49 M circle dot, respectively. The companion mass to PSR J0218+4232 was found to be 0.179 - 0.016 + 0.018 M circle dot. We constrained the mass of the neutron star companion of PSR J1518+4904 to be 1.248 - 0.029 + 0.035 M circle dot, 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 circle dot; 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 P b = 0.14 ( 2 ) x 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.