A high time resolution study of the millisecond pulsar J2241-5236 at frequencies below 300 MHz

Abstract

One of the major challenges for pulsar timing array (PTA) experiments is the mitigation of the effects of the turbulent interstellar medium (ISM) from timing data. These can potentially lead to measurable delays and/or distortions in the pulse profiles and scale strongly with the inverse of the radio frequency. Low-frequency observations are therefore highly appealing for characterizing them. However, in order to achieve the necessary time resolution to resolve profile features of short-period millisecond pulsars, phase-coherent de-dispersion is essential, especially at frequencies below $300$ MHz. We present the lowest-frequency ($80$-$220$ MHz), coherently de-dispersed detections of one of the most promising pulsars for current and future PTAs, PSR J2241$-$5236, using our new beam-former software for the MWA's voltage capture system (VCS), which reconstructs the time series at a much higher time resolution of $\sim 1\mu$s by re-synthesizing the recorded voltage data at $10$-kHz/$100$-$\mu$s native resolutions. Our data reveal a dual-precursor type feature in the pulse profile that is either faint or absent in high-frequency observations from Parkes. The resultant high-fidelity detections have enabled dispersion measure (DM) determinations with very high precision, of the order of $(2$-$6)\times 10^{-6}$ $\mathrm{pc}\mathrm{c}{\mathrm{m}}^{-3}$, owing to the microsecond level timing achievable for this pulsar at the MWA's low frequencies. This underscores the usefulness of low-frequency observations for probing the ISM toward PTA pulsars and informing optimal observing strategies for PTA experiments.

arXiv comment09 pages, 4 figures, 2 tables

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• High Precision Measurements of Interstellar Dispersion Measure with the upgraded GMRT
• Discovery of a steep-spectrum low-luminosity pulsar with the Murchison Widefield Array
• Detection of frequency-dependent dispersion measure toward the millisecond pulsar PSR J2241-5236 from contemporaneous wide-band observations
• An Ultra-High Time Resolution Cosmic Ray Detection Mode for the Murchison Widefield Array
• Independent discovery of a nulling pulsar with unusual sub-pulse drifting properties with the Murchison Widefield Array