Modelling and mitigating refractive propagation effects in precision pulsar timing observations

TL;DR

This paper investigates how large-scale electron-density variations in the interstellar medium affect pulsar timing precision, highlighting the limitations of current correction methods, especially at low radio frequencies, due to stochastic propagation effects.

Contribution

It introduces a simulation-based assessment of propagation effects and identifies stochastic timing perturbations that challenge existing correction techniques in pulsar timing.

Findings

Large-scale density variations cause non-stationary timing perturbations.

Frequency-dependent wave trajectories introduce stochastic effects.

Low-frequency observations are less effective for high dispersion measure pulsars.

Abstract

To obtain the most accurate pulse arrival times from radio pulsars, it is necessary to correct or mitigate the effects of the propagation of radio waves through the warm and ionised interstellar medium. We examine both the strength of propagation effects associated with large-scale electron-density variations and the methodology used to estimate infinite-frequency arrival times. Using simulations of two-dimensional phase-varying screens, we assess the strength and non-stationarity of timing perturbations associated with large-scale density variations. We identify additional contributions to arrival times that are stochastic in both radio frequency and time and therefore not amenable to correction solely using times of arrival. We attribute this to the frequency dependence of the trajectories of the propagating radio waves. We find that this limits the efficacy of low-frequency (metre-wavelength) observations. Incorporating low-frequency pulsar observations into precision timing campaigns is increasingly problematic for pulsars with larger dispersion measures.