A study of 80 known pulsars at 185 MHz using MWA incoherent drift-scan observations

TL;DR

This study reprocesses 48 archival MWA-VCS drift-scan observations at 185 MHz with a PRESTO-based pipeline to conduct a wide-field census of known pulsars. It detects 80 pulsars (including 30 with first-time 185 MHz measurements) over ~30,000 deg$^2$, achieving a best sensitivity near $8$ mJy. Flux densities for 77 pulsars largely agree with extrapolations from higher frequencies, while broadband spectral analyses reveal 47 low-frequency turnovers and only 6 SSA-consistent cases, implying multiple absorption mechanisms. Scattering analyses show generally shallower-than-Kolmogorov indices and require hybrid PBFs for complex lines of sight, with the $W_{10}$–$P_0$ relation at low frequency aligning with prior work. The results establish crucial baselines for low-frequency pulsar emission and ISM studies and outline practical pathways for SKA-Low-era surveys, including multi-frequency campaigns and polarization studies.

Abstract

A systematic study of 80 known pulsars observed at 185 MHz has been conducted using archival incoherent-sum data from the Murchison Widefield Array (MWA). The dataset comprises 48 drift-scan observations from the MWA Voltage Capture System, covering approximately 30,000 square degrees of sky with sensitivities reaching about 8 mJy in the deepest regions. An optimized PRESTO-based search pipeline was deployed on the China SKA Regional Centre infrastructure. This enabled the detection of 80 known pulsars, representing a 60 percent increase over the previous census. Notably, this includes 30 pulsars with first-time detections at this frequency, of which pulse profiles and flux densities are presented. Spectral, scattering, and pulse-width properties were examined for the sample, providing observational constraints on low-frequency turnover, propagation effects, and width-period relations. This study highlights the value of wide-field, low-frequency time-domain surveys for constraining pulsar emission and propagation, offering empirical insights that may inform future observations with instruments such as SKA-Low.

Figures (9)

• Figure 1: Pulsar search pipeline for the MWA-VCS incoherent-sum data.
• Figure 2: The sensitivity map includes sidelobes with beam power above 1% of $G_{\text{zenith}}$. The detection threshold corresponds to $S/N_{\text{min}} = 4$, assuming a 3% duty cycle. Our search methodology successfully identified 80 known pulsars marked in red stars.
• Figure 3: Comparison of measured 185 MHz flux densities ($S_{\text{185}}$) with expected values ($S_{\text{exp}}$) extrapolated from $\nu \geq 400$ MHz power-law spectra in the ATNF catalog. The red line represents unity ($S_{\text{185}} = S_{\text{exp}}$), and the grey band indicates the $1\sigma$ uncertainty range, centered on the best-fit ratio $S_{\text{185}}/S_{\text{exp}} = 0.96^{+0.11}_{-0.09}$
• Figure 4: SSA model fits for six pulsars, showing the best-fit results based on archival and our measured flux densities
• Figure 5: The shaded regions show 2D kernel density estimates (KDE). The red circles mark the sources with the best-fit SSA model. The red and blue lines indicate the OLS and the ORD fittings, respectively, with their $1\sigma$ uncertainties from bootstrapping.