The Southern-sky MWA Rapid Two-metre (SMART) pulsar survey -- III. A census of millisecond pulsars at 154 MHz

TL;DR

This study presents a low-frequency survey of millisecond pulsars in the southern sky at 154 MHz, detecting 40 MSPs including 11 new below 300 MHz, providing detailed polarization and RM measurements to enhance understanding of their emission and interstellar effects.

Contribution

First comprehensive low-frequency MSP census in the southern hemisphere at 154 MHz, including new detections and detailed polarization and RM data.

Findings

Detected 40 MSPs, 11 of which are new below 300 MHz.

Found significant Faraday rotation measures for 25 MSPs.

Observed increased polarization at low frequencies.

Abstract

Observations of millisecond pulsars (MSPs) at low radio frequencies play an important role in understanding the Galactic pulsar population and characterising both their emission properties and the effects of the ionised interstellar medium on the received signals. To date, only a relatively small fraction of the known MSP population has been detected at frequencies below 300 MHz, and nearly all previous MSP studies at these frequencies have been conducted with northern telescopes. We present a census of MSPs in the SMART pulsar survey, covering declinations south of +30 deg at a centre frequency of 154 MHz. We detected 40 MSPs, with 11 being the first published detections below 300 MHz. For each detection, we provide coherently-dedispersed full-polarimetric integrated pulse profiles and mean flux densities. We measured significant Faraday rotation measures (RMs) for 25 MSPs, and identified apparent phase-dependent RM variations for three MSPs. Comparison with published profiles at other frequencies supports previous studies suggesting that the pulse component separations of MSPs vary negligibly over a wide frequency range due to their compact magnetospheres. We observe that integrated pulse profiles tend to be more polarised at low frequencies, consistent with depolarisation due to superposed orthogonal polarisation modes. The results of this census will be a valuable resource for planning future MSP monitoring projects at low frequencies, and will also help to improve survey simulations to forecast the detectable MSP population with the SKA-Low.