Scattering of pulsar radio emission by the interstellar plasma

TL;DR

This paper uses simulations to explore how interstellar plasma scattering affects pulsar radio signals, revealing the significant role of dispersion and refraction, and demonstrating methods to correct timing fluctuations in observations.

Contribution

It introduces a simulation approach to analyze complex scattering phenomena, highlighting the combined effects of dispersion and refraction on pulsar timing and proposing correction techniques.

Findings

Dispersion significantly influences scattering effects.

Timing fluctuations can be partially corrected using intensity and dispersion measurements.

Observed fluctuations are larger than expected from simple turbulence models.

Abstract

We present simulations of scattering phenomena which are important in pulsar observations, but which are analytically intractable. The simulation code, which has also been used for solar wind and atmospheric scattering problems, is available from the authors. These simulations reveal an unexpectedly important role of dispersion in combination with refraction. We demonstrate the effect of analyzing observations which are shorter than the refractive scale. We examine time-of-arrival fluctuations in detail: showing their correlation with intensity and dispersion measure; providing a heuristic model from which one can estimate their contribution to pulsar timing observations; and showing that much of the effect can be corrected making use of measured intensity and dispersion. Finally, we analyze observations of the millisecond pulsar J0437$-$4715, made with the Parkes radio telescope, that show timing fluctuations which are correlated with intensity. We demonstrate that these timing fluctuations can be corrected, but we find that they are much larger than would be expected from scattering in a homogeneous turbulent plasma with isotropic density fluctuations. We do not have an explanation for these timing fluctuations.