Imaging pulsar census of the Galactic Plane using MWA VCS data

TL;DR

This study develops an image-based pulsar detection pipeline using MWA VCS data, enabling the discovery of pulsars undetectable by traditional methods at low frequencies, thus expanding the known pulsar population in the Galactic Plane.

Contribution

The paper introduces a novel image-based pulsar census method at low frequencies, revealing pulsars missed by traditional time-domain searches and providing new low-frequency detections.

Findings

Detected 83 known pulsars, including 16 only in images

First low-frequency detections for 14 pulsars

Highlights importance of image-based searches at low frequencies

Abstract

Traditional pulsar surveys have primarily employed time-domain periodicity searches. However, these methods are susceptible to effects like scattering, eclipses and orbital motion. At lower radio frequencies (<= 300 MHz), factors such as dispersion measure and pulse broadening become more prominent, reducing the detection sensitivity. On the other hand, image domain searches for pulsars are not limited by these effects and can extend the parameter space to regions inaccessible to traditional search techniques. Therefore, we have developed a pipeline to form 1-second full Stokes images from offline correlated high time-resolution data from the Murchison Widefield Array (MWA). This led to the development of image-based methodologies to identify new pulsar candidates. In this paper, we applied these methodologies to perform a low-frequency image-based pulsar census of the Galactic Plane ( 12 MWA observations, covering ~6000 deg^2 sky ). This work focuses on the detection of the known pulsar population which were present in the observed region of the sky using both image-based and beamformed methods. This resulted in the detection of 83 known pulsars, with 16 pulsars found only in Stokes I images but not in periodicity searches applied in beamformed data. Notably, for 14 pulsars these are the first reported low-frequency detections. This underscores the importance of image-based searches for pulsars that may be undetectable in time-series data, due to scattering and/or dispersive smearing at low frequencies. This highlights the importance of low-frequency flux density measurements in refining pulsar spectral models and investigating the spectral turnover of pulsars at low frequencies.