2025MNRAS.538.2923D

PSR B1828-11 is a radio pulsar that undergoes periodic modulations (∼500 d) of its spin-down rate and beamwidth, providing a valuable opportunity to understand the rotational dynamics of neutron stars. The periodic modulations have previously been attributed to planetary companion(s), precession, or magnetospheric effects and have several interesting features: they persist over 10 cycles, there are at least two harmonically related components, and the period is decreasing at a rate of about 5 d per cycle. PSR B1828-11 also experienced a glitch, a sudden increase in its rotation frequency, at $55040.9 \,{\rm MJD}$. By studying the interaction of the periodic modulations with the glitch, we seek to find evidence to distinguish explanations of the periodic modulation. Using a phenomenological model, we analyse a data set from Jodrell Bank Observatory, providing the longest and highest resolution measurements of the pulsar's spin-down rate data. Our phenomenological model consists of step changes in the amplitude, modulation frequency, and phase of the long-term periodic modulation and the usual spin-down glitch behaviour. We find clear evidence with a (natural-log) Bayes factor of 1486 to support that not only is there a change to these three separate parameters but that the shifts occur before the glitch. We also present model-independent evidence which demonstrates visually how and when the modulation period and amplitude change. Discontinuities in the modulation period are difficult to explain if a planetary companion sources the periodic modulations, but we conclude with a discussion on the insights into precession and magnetospheric switching.