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

## TL;DR

This study demonstrates high time resolution, low-frequency observations of pulsar J2241-5236 using coherent de-dispersion, revealing new pulse profile features and enabling precise interstellar medium measurements crucial for pulsar timing arrays.

## Contribution

The paper introduces a new beam-former software for the MWA that achieves microsecond time resolution at frequencies below 300 MHz, enabling detailed pulse profile analysis and high-precision dispersion measure estimation.

## Key findings

- Revealed a dual-precursor feature in the pulse profile at low frequencies.
- Achieved dispersion measure precision of (2-6)×10⁻⁶ pc cm⁻³.
- Demonstrated the effectiveness of low-frequency, high-resolution observations for probing the interstellar medium.

## 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 $(2$-$6)\times10^{-6}$ $\rm pc\,cm^{-3}$, 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.