Resolving discrete pulsar spin-down states with current and future instrumentation

TL;DR

This paper investigates the ability of current and future pulsar observation techniques to detect discrete changes in pulsar spin-down rates, highlighting limitations and potential improvements for resolving rapid, small-scale transitions.

Contribution

The study uses simulations to assess the detectability of $ u$-rate transitions in pulsars and proposes methods to improve detection with upcoming sensitive radio telescopes.

Findings

Current methods are insensitive to small, rapid $ u$-rate changes.

Pulse shape analysis can improve transition detection in some cases.

Cadence impacts detectability, but future telescopes can mitigate this issue.

Abstract

An understanding of pulsar timing noise offers the potential to improve the timing precision of a large number of pulsars as well as facilitating our understanding of pulsar magnetospheres. For some sources, timing noise is attributable to a pulsar switching between two different spin-down rates $(\dot{\nu})$. Such transitions may be common but difficult to resolve using current techniques. In this work, we use simulations of $\dot{\nu}$-variable pulsars to investigate the likelihood of resolving individual $\dot{\nu}$ transitions. We inject step-changes in the value of $\dot{\nu}$ with a wide range of amplitudes and switching timescales. We then attempt to redetect these transitions using standard pulsar timing techniques. The pulse arrival-time precision and the observing cadence are varied. Limits on $\dot{\nu}$ detectability based on the effects such transitions have on the timing residuals are derived. With the typical cadences and timing precision of current timing programs, we find we are insensitive to a large region of $\Delta \dot{\nu}$ parameter space which encompasses small, short timescale switches. We find, where the rotation and emission states are correlated, that using changes to the pulse shape to estimate $\dot{\nu}$ transition epochs, can improve detectability in certain scenarios. The effects of cadence on $\Delta \dot{\nu}$ detectability are discussed and we make comparisons with a known population of intermittent and mode-switching pulsars. We conclude that for short timescale, small switches, cadence should not be compromised when new generations of ultra-sensitive radio telescopes are online.