Detection of frequency-dependent dispersion measure toward the millisecond pulsar PSR J2241-5236 from contemporaneous wide-band observations

TL;DR

This study detects frequency-dependent dispersion measures in pulsar PSR J2241-5236 using wide-band observations from 80 MHz to 4 GHz, highlighting implications for pulsar timing precision and PTA efforts.

Contribution

It presents the first detection of chromatic dispersion measure variations across a broad frequency range in a millisecond pulsar, utilizing simultaneous observations from multiple radio telescopes.

Findings

Measured DM changes scale as ν^{2.5 ± 0.1}

Demonstrated the importance of low-frequency data for PTA precision

Highlighted potential impacts on pulsar timing noise budgets

Abstract

Making precise measurements of pulsar dispersion measures (DMs) and applying suitable corrections for them is amongst the major challenges in high-precision timing programmes such as pulsar timing arrays (PTAs). While the advent of wide-band pulsar instrumentation can enable more precise DM measurements and thence improved timing precision, it also necessitates doing careful assessments of frequency-dependent (chromatic) DMs that was theorised by Cordes et al. (2016). Here we report the detection of such an effect in broadband observations of the millisecond pulsar PSR J2241-5236, a high-priority target for current and future PTAs. The observations were made contemporaneously using the wide-band receivers and capabilities now available at the Murchison Widefield Array (MWA), the upgraded Giant Metrewave Radio Telescope (uGMRT) and the Parkes telescopes, thus providing an unprecedentedly large frequency coverage from 80 MHz to 4 GHz. Our analysis shows the measurable changes in DM that scale with the observing frequency ($\nu$) as $\rm \delta DM \sim \nu^{2.5 \pm 0.1}$. We discuss the potential implications of such a frequency dependence in the measured DMs, and the likely impact on the timing noise budget, and comment on the usefulness of low-frequency observations in advancing PTA efforts.