Long-term rotational and emission variability of 17 radio pulsars

Abstract

ABSTRACT With the ever-increasing sensitivity and timing baselines of modern radio telescopes, a growing number of pulsars are being shown to exhibit transitions in their rotational and radio emission properties. In many of these cases, the two are correlated with pulsars assuming a unique spin-down rate ($\dot{\nu }$) for each of their specific emission states. In this work, we revisit 17 radio pulsars previously shown to exhibit spin-down rate variations. Using a Gaussian process regression (GPR) method to model the timing residuals and the evolution of the profile shape, we confirm the transitions already observed and reveal new transitions in 8 yr of extended monitoring with greater time resolution and enhanced observing bandwidth. We confirm that seven of these sources show emission-correlated $\dot{\nu }$ transitions ($\Delta \dot{\nu }$), and we characterize this correlation for one additional pulsar, PSR B1642−03. We demonstrate that GPR is able to reveal extremely subtle profile variations given sufficient data quality. We also corroborate the dependence of $\Delta \dot{\nu }$ amplitude on $\dot{\nu }$ and pulsar characteristic age. Linking $\Delta \dot{\nu }$ to changes in the global magnetospheric charge density Δρ, we speculate that $\dot{\nu }$ transitions associated with large Δρ values may be exhibiting detectable profile changes with improved data quality, in cases where they have not previously been observed.