Timing of young radio pulsars I: Timing noise, periodic modulation and proper motion

Abstract

The smooth spin-down of young pulsars is perturbed by two non-deterministic phenomenon, glitches and timing noise. Although the timing noise provides insights into nuclear and plasma physics at extreme densities, it acts as a barrier to high-precision pulsar timing experiments. An improved methodology based on Bayesian inference is developed to simultaneously model the stochastic and deterministic parameters for a sample of 85 high-$\dot{E}$ radio pulsars observed for $\sim$ 10 years with the 64-m Parkes radio telescope. Timing noise is known to be a red process and we develop a parametrization based on the red-noise amplitude ($A_{\mathrm{red}}$) and spectral index ($\beta$). We measure the median $A_{\mathrm{red}}$ to be $-10.4_{-1.7}^{+1.8}$ yr${}^{3/2}$ and $\beta$ to be $-5.2_{-3.8}^{+3.0}$ and show that the strength of timing noise scales proportionally to ${\nu }^1|\dot{\nu }{|}^{-0.6\pm 0.1}$, where $\nu$ is the spin frequency of the pulsar and $\dot{\nu }$ its spin-down rate. Finally, we measure significant braking indices for 19 pulsars, proper motions for two pulsars and discuss the presence of periodic modulation in the arrival times of five pulsars.