Long-term rotational and emission variability of 17 radio pulsars

B. Shaw, B. W. Stappers, P. Weltevrede, P. R. Brook, A. Karastergiou, C. A. Jordan, M. J. Keith, M. Kramer, A. G. Lyne

Published 2022-04-22Version 1

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 years of extended monitoring with greater time resolution and enhanced observing bandwidth. We confirm that 7 of these sources show emission-correlated $\dot{\nu}$ transitions ($\Delta \dot{\nu}$) 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 $\Delta \dot{\nu}$ amplitude on $\dot{\nu}$ and pulsar characteristic age. Linking $\Delta \dot{\nu}$ to changes in the global magnetospheric charge density $\Delta \rho$, we speculate that $\dot{\nu}$ transitions associated with large $\Delta \rho$ values may be exhibiting detectable profile changes with improved data quality, in cases where they have not previously been observed.