High-cadence Timing of Binary Pulsars with CHIME

Abstract

We performed near-daily observations on 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 years of CHIME/Pulsar timing data. We measured the pulsar masses to be $1.49_{-0.20}^{+0.23}$ M${}_{\odot }$, $1.470_{-0.034}^{+0.030}$ M${}_{\odot }$ and $1.50_{-0.38}^{+0.49}$ M${}_{\odot }$ respectively. The companion mass to PSR J0218+4232 was found to be $0.179_{-0.016}^{+0.018}$ M${}_{\odot }$. We constrained the mass of the neutron-star companion of PSR J1518+4904 to be $1.248_{-0.029}^{+0.035}$ M${}_{\odot }$, using the observed apsidal motion as a constraint on mass estimation. The binary companion to PSR J2023+2853 was found to have a mass of $0.93_{-0.14}^{+0.17}$ M${}_{\odot }$; 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 $\dot{P_{\mathrm{b}}}=0.14(2)\times 10^{-12}$; we determined that this variation arises from ``Shklovskii acceleration" due to relative motion of the binary system, and used this measurement to estimate a distance of $d=(6.7\pm 1.0)$ 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.

14 pages, 4 figures, accepted for publication in ApJ