Improving DM estimates using low-frequency scattering-broadening estimates

TL;DR

This paper introduces a new method to improve pulsar dispersion measure estimates by using low-frequency scattering-broadening data, effectively reducing bias caused by interstellar medium effects and enhancing pulsar timing precision.

Contribution

The authors develop and validate a technique that corrects for scattering-induced delays, providing unbiased DM measurements and characterizing scattering parameters from real pulsar data.

Findings

The method removes bias in simulated DM estimates with high signal-to-noise ratio.

Scattering parameters vary over time and differ from Kolmogorov turbulence expectations.

Application to PSR J1643-1224 yields insights into interstellar scattering properties.

Abstract

A pulsar's pulse profile gets broadened at low frequencies due to dispersion along the line of sight or due to multi-path propagation. The dynamic nature of the interstellar medium makes both of these effects time-dependent and introduces slowly varying time delays in the measured times-of-arrival similar to those introduced by passing gravitational waves. In this article, we present an improved method to correct for such delays by obtaining unbiased dispersion measure (DM) measurements by using low-frequency estimates of the scattering parameters. We evaluate this method by comparing the obtained DM estimates with those, where scatter-broadening is ignored using simulated data. A bias is seen in the estimated DMs for simulated data with pulse-broadening with a larger variability for a data set with a variable frequency scaling index, $\alpha$, as compared to that assuming a Kolmogorov turbulence. Application of the proposed method removes this bias robustly for data with band averaged signal-to-noise ratio larger than 100. We report the measurements of the scatter-broadening time and $\alpha$ from analysis of PSR J1643$-$1224, observed with upgraded Giant Metrewave Radio Telescope as part of the Indian Pulsar Timing Array experiment. These scattering parameters were found to vary with epoch and $\alpha$ was different from that expected for Kolmogorov turbulence. Finally, we present the DM time-series after application of this technique to PSR J1643$-$1224.