Observations of Low-Frequency Radio Emission from Millisecond Pulsars and Multipath Propagation in the Interstellar Medium

Abstract

Studying the gravitational-wave sky with pulsar timing arrays (PTAs) is a key science goal for the Square Kilometre Array (SKA) and its pathfinder telescopes. With current PTAs reaching sub-microsecond timing precision, making accurate measurements of interstellar propagation effects and mitigating them effectively has become increasingly important to realise PTA goals. As these effects are much stronger at longer wavelengths, low-frequency observations are most appealing for characterizing the interstellar medium (ISM) along the sight lines toward PTA pulsars. The Murchison Widefield Array (MWA) and the Engineering Development Array (EDA), which utilizes MWA technologies, present promising opportunities for undertaking such studies, particularly for PTA pulsars located in the southern sky. Such pulsars are also the prime targets for PTA efforts planned with the South African MeerKAT, and eventually with the SKA. In this paper we report on observations of two bright southern millisecond pulsars PSRs J0437-4715 and J2145-0750 made with these facilities; MWA observations sampling multiple frequencies across the 80-250 MHz frequency range, while the EDA providing direct-sampled baseband data to yield a large instantaneous usable bandwidth of $\sim$200 MHz. Using these observations, we investigate various aspects relating to pulsar emission and ISM properties, such as spectral evolution of the mean pulse shape, scintillation as a function of frequency, chromaticity in interstellar dispersion, and flux density spectra at low frequencies. Systematic and regular monitoring observations will help ascertain the role of low-frequency measurements in PTA experiments, while simultaneously providing a detailed characterization of the ISM toward the pulsars, which will be useful in devising optimal observing strategies for future PTA experiments.

arXiv comment23 pages, 10 Figures, 4 Tables, Accepted to ApJS

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• The Engineering Development Array: A low frequency radio telescope utilising SKA precursor technology
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Cited by in corpus (18)

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• Pulsars with NenuFAR: backend and pipelines
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• MWA Tied-Array Processing I: Calibration and Beamformation
• Discovery of a steep-spectrum low-luminosity pulsar with the Murchison Widefield Array
• MWA tied-array processing III: Microsecond time resolution via a polyphase synthesis filter
• A high time resolution study of the millisecond pulsar J2241-5236 at frequencies below 300 MHz
• A search for radio pulsars in five nearby supernova remnants
• Discovery and follow-up of a quasiperiodically nulling and sub-pulse drifting pulsar with the Murchison Widefield Array
• Detection of frequency-dependent dispersion measure toward the millisecond pulsar PSR J2241-5236 from contemporaneous wide-band observations
• A Cyclic Spectroscopy Scintillation Study of PSR B1937+21 I. Demonstration of Improved Scintillometry
• Impact of the observation frequency coverage on the significance of a gravitational wave background detection in PTA data
• A Simultaneous Dual-Frequency Scintillation Arc Survey of Six Bright Canonical Pulsars Using the Upgraded Giant Metrewave Radio Telescope
• Evaluating Low-Frequency Pulsar Observations to Monitor Dispersion with the Giant Metrewave Radio Telescope
• Independent discovery of a nulling pulsar with unusual sub-pulse drifting properties with the Murchison Widefield Array