Long-term rotational and emission variability of 17 radio pulsars

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 ($\dotν$) 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 years of extended monitoring with greater time resolution and enhanced observing bandwidth. We confirm that 7 of these sources show emission-correlated $\dotν$ transitions ($Δ\dotν$) and we characterise 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 $Δ\dotν$ amplitude on $\dotν$ and pulsar characteristic age. Linking $Δ\dotν$ to changes in the global magnetospheric charge density $Δρ$, we speculate that $\dotν$ 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.