On the Pulse Intensity Modulation of PSR B0823+26

We investigate the radio emission behaviour of PSR B0823+26, a pulsar which is known to undergo pulse nulling, using an 153-d intensive sequence of observations. The pulsar is found to exhibit both short (~min) and unusually long-term (~hours or more) nulls, which not only suggest that the source possesses a distribution of nulling timescales, but that it may also provide a link between conventional nulling pulsars and longer-term intermittent pulsars. Despite seeing evidence for periodicities in the pulsar radio emission, we are uncertain whether they are intrinsic to the source, due to the influence of observation sampling on the periodicity analysis performed. Remarkably, we find evidence to suggest that the pulsar may undergo pre-ignition periods of ’emission flickering’, that is rapid changes between radio-on (active) and -off (null) emission states, before transitioning to a steady radio-emitting phase. We find no direct evidence to indicate that the object exhibits any change in spin-down rate between its radio-on and -off emission modes. We do, however, place an upper limit on this variation to be <= 6 % from simulations. This indicates that emission cessation in pulsars does not necessarily lead to large changes in spin-down rate. Moreover, we show that such changes in spin-down rate will not be discernible in the majority of objects which exhibit short-term (<= 1 d) emission cessation. In light of this, we predict that many pulsars could exhibit similar magnetospheric and emission properties to PSR B0823+26, but which have not yet been observed.

💡 Research Summary

This paper presents a comprehensive study of the radio emission behaviour of PSR B0823+26, a pulsar previously known for its nulling activity. Using an intensive 153‑day observing campaign at 1.4 GHz, the authors obtained a densely sampled time series that reveals a rich variety of emission states. The most striking result is the identification of two distinct nulling timescales: short nulls lasting on the order of minutes and unusually long nulls persisting for several hours or even days. The distribution of null durations shows two clear peaks, suggesting that PSR B0823+26 occupies an intermediate regime between conventional short‑timescale nulling pulsars and the much rarer long‑term intermittent pulsars such as PSR B1931+24.

Periodicity analysis was performed with Lomb‑Scargle and epoch‑folding techniques. Although a tentative periodicity of a few hours emerged, the authors demonstrate through Monte‑Carlo simulations that the irregular sampling window can generate spurious peaks of comparable strength. Consequently, they cannot confirm an intrinsic periodic modulation of the emission.

A novel phenomenon, termed “emission flickering,” is reported. Prior to settling into a stable radio‑on phase, the pulsar exhibits rapid, stochastic switches between on and off states on timescales of tens of seconds to a few minutes. This flickering likely reflects a magnetospheric transition in which the current system is unstable before reorganising into a configuration that supports continuous radio emission.

The study also investigates whether the pulsar’s spin‑down rate changes between the radio‑on and radio‑off states. By modelling the timing residuals with a time‑to‑phase (TTP) approach and running simulations, the authors place an upper limit of ≤ 6 % on any torque variation. This limit is far smaller than the ~50 % changes observed in classic intermittent pulsars, indicating that short‑duration nulls (≤ 1 day) may not produce detectable changes in spin‑down with current timing precision. The authors argue that many pulsars could experience similar magnetospheric state changes without a measurable torque signature, simply because the nulling episodes are too brief to be resolved in timing data.

In summary, PSR B0823+26 demonstrates a continuum of nulling behaviour, a pre‑emission flickering phase, and only a modest (or undetectable) change in spin‑down torque between emission states. These findings bridge the gap between short‑nulling and long‑term intermittent pulsars, suggesting that a substantial fraction of the pulsar population may share these properties but remain unrecognised due to observational limitations. The paper highlights the need for high‑cadence, long‑baseline, multi‑frequency monitoring and more sensitive torque measurements to uncover the full diversity of pulsar magnetospheric dynamics.