Discovery of radio eclipses from 4FGL J1646.5-4406: a new candidate redback pulsar binary
Abstract
Large widefield surveys make possible the serendipitous discovery of rare subclasses of pulsars. One such class are 'spider'-type pulsar binaries, comprised of a pulsar in a compact orbit with a low-mass (sub)stellar companion. In a search for circularly polarized radio sources in Australian Square Kilometre Array Pathfinder (ASKAP) Pilot Survey observations, we discovered highly variable and circularly polarized emission from a radio source within the error region of the γ-ray source 4FGL J1646.5-4406. The variability is consistent with the eclipse of a compact, steep-spectrum source behind ablated material from a companion in an ~5.3 h binary orbit. Based on the eclipse properties and spatial coincidence with 4FGL J1646.5-4406, we argue that the source is likely a recycled pulsar in a 'redback' binary system. Using properties of the eclipses from ASKAP and Murchison Widefield Array observations, we provide broad constraints on the properties of the eclipse medium. We identified a potential optical/infrared counterpart in archival data consistent with a variable low-mass star. Using the Parkes radio telescope 'Murriyang' and the Meer Karoo Array Telescope (MeerKAT) , we searched extensively for radio pulsations but yielded no viable detections of pulsed emission. We suggest that the non-detection of pulses is due to scattering in the intra-binary material, but scattering from the interstellar medium can also plausibly explain the pulse non-detections if the interstellar dispersion measure exceeds ~600 pc cm-3. Orbital constraints derived from optical observations of the counterpart would be highly valuable for future γ-ray pulsation searches, which may confirm the source nature as a pulsar.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2024
- DOI:
- 10.1093/mnras/stae033
- arXiv:
- arXiv:2312.00261
- Bibcode:
- 2024MNRAS.528.5730Z
- Keywords:
-
- binaries: eclipsing;
- pulsars: general;
- radio continuum: transients;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Submitted to MNRAS. 13 Pages, 10 figures, 3 tables