Evolutionary Map of the Universe: A pilot survey to detect high Galactic latitude pulsars in variance images with ASKAP

TL;DR

This paper demonstrates a pilot variance-imaging survey with ASKAP-EMU to detect high-Galactic-latitude pulsars. By constructing variance images from snapshot continuum data and conducting targeted follow-up with Murriyang, the authors identify two new pulsars (P = $85.707$ ms, DM $=19.4$ cm$^{-3}$ pc; P = $5.492$ ms, DM $=29.5$ cm$^{-3}$ pc) and a third pulsar (P = $14.828$ ms, DM $=39.0$ cm$^{-3}$ pc), along with known pulsars and radio-star candidates. They develop an end-to-end variance-imaging pipeline, validate candidates via dynamic spectra and polarization, and discuss limitations (PSF variations, sidelobes) and improvements (peeling, self-calibration, WSClean) for applying the method to the full EMU sky and future SKA-era surveys. The results demonstrate variance imaging as a powerful, scalable approach to uncover scintillating pulsars, especially MSPs and binaries, in wide-field continuum data at ~1 GHz.

Abstract

It has been proposed that radio pulsars can be distinguished from other point-like radio sources in continuum images by their unique interstellar scintillation signatures. Using data from the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey, we conducted a pilot survey of radio pulsars at high Galactic latitude regions via the variance imaging method. Out of approximately 59,800 compact radio sources detected in a ~480 square degree survey area, we identified 20 highly variable sources. Among them, 9 are known pulsars, 1 is a known radio star, 1 is an ultra-long period source, 3 are radio star candidates, and the remaining 6 are pulsar candidates. Notably, we discovered two strongly scintillating pulsars: one with a period of 85.707 ms and a dispersion measure (DM) of 19.4 pc/cm^3, and another with a period of 5.492 ms and a DM of 29.5 pc/cm^3. In addition, a third pulsar was discovered in the variance images, with a period of 14.82 ms and a DM of 39.0 pc/cm^3. This source shows a steep radio spectrum and a high degree of circular polarisation. These results underscore the strong potential of variance imaging for pulsar detection in full EMU and future radio continuum surveys planned with Square Kilometre Array (SKA).

Figures (7)

• Figure 1: Left: A portion of the radio-continuum image of the tile SB 61946 at 943.5 MHz. The field of view is 2$\times$2 deg$^{2}$. The white region at the bottom-left corner lies outside the FWHM for the primary beam, which is approximately $1.5^\circ$. The beam size of the radio image is 15 arcsec $\times$ 15 arcsec and shown at the bottom left corner. The color bar is in units of Jy beam$^{-1}$. Right: The corresponding variance image (beam 05) containing the new pulsar J2223--0654 in a suqare box. The region of enhanced variance at the top left corner is due to the sidelobes of an out-of-beam bright source.
• Figure 2: Distribution of sources in variance images for tiles where pulsar and radio star candidates are detected. Known pulsars (with tag PSR) and candidates are shown as blue squares. The sources labelled as red are detected in variance images but not picked up by our 5$\sigma$ threshold explained in Section \ref{['sec:select']}.
• Figure 3: Variance images (left) and dynamic spectra (right) of known pulsars, radio star (J1200--4929), and LPT source akr+25 detected in variance images. The continuum source J1704--6019 is potentially associated with PSR J1704--6016 as reported in wng+23.
• Figure 4: Variance images (left) and dynamic spectra (right) of pulsar and radio star candidates (J0919--7738, J1255--5133, and J1813--6047) detected in variance images.
• Figure 5: Murriyang dynamic spectra of PSRs J0927--7641, J1838--5949 and J2223--0654.