Flux density monitoring of 89 millisecond pulsars with MeerKAT

We present a flux density study of 89 millisecond pulsars (MSPs) regularly monitored as part of the MeerKAT Pulsar Timing Array (MPTA) using the L-Band receiver with an approximately two week cadence between 2019 and 2022. For each pulsar, we have determined the mean flux densities at each epoch in eight similar to 97 MHz sub-bands ranging from 944 to 1625 MHz. From these we have derived their modulation indices, their average and peak-to-median flux densities in each sub-band, as well as their mean spectral indices across the entire frequency range. We find that the vast majority of the MSPs have spectra that are well described by a simple power law, with a mean spectral index of -1.86(6). Using the temporal variation of the flux densities, we measured the structure functions and determined the refractive scintillation time-scale for seven. The structure functions provide strong evidence that the intrinsic radio luminosities of MSPs are stable. As a population, the average modulation index at 20 cm wavelengths peaks near unity at dispersion measures (DMs) of similar to 20 pc cm(-3) and by a DM of 100 pc cm(-3) are closer to 0.2, due to refractive scintillation. We find that timing arrays can improve their observing efficiency by reacting to scintillation maxima, and that 20 cm FRB surveys should prioritize highly scintillating mid-latitude regions of the Galactic sky where they will find similar to 30 per cent more events and bursts at greater distances.

Automated summary

This study presents a flux density analysis of 89 millisecond pulsars (MSPs) monitored as part of the MeerKAT Pulsar Timing Array (MPTA). The analysis reveals that most MSPs have spectra that can be described by a simple power law, and their intrinsic radio luminosities are stable. Observations of refractive scintillation lead to recommendations for improved efficiency in timing arrays and prioritization of highly scintillating regions for 20 cm Fast Radio Burst (FRB) surveys.