White Dwarf Binary Identified as Source of Long-Period Radio Transients

An international research team led by the University of Sydney used the Australian Square Kilometre Array Pathfinder (ASKAP) to locate the origin of a long-period radio transient (LPT). The object, catalogued as ASKAP J174508.9-505149 and also referred to as ASKAP J1745-5051, exhibits periodic radio bursts that repeat every 1.345 hours. Spectroscopic observations confirmed the source is a magnetic cataclysmic variable: a white dwarf accreting material from a close companion.

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LPTs are strong radio bursts that recur on timescales of minutes to hours. About a dozen have been detected in the Milky Way, but their nature has remained uncertain. Earlier hypotheses favored slowly rotating magnetars or white-dwarf binaries; magnetar models conflict with theory, and prior binary candidates lacked direct accretion evidence.

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The study involved doctoral student Kovi Rose of the University of Sydney’s School of Physics and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), with observations from ASKAP, a wide-field radio telescope. The collaboration included institutions across Australia and other countries.

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Spectroscopy showed hydrogen Balmer-series and helium (He I, He II) emission lines; the strong He II line is characteristic of magnetic cataclysmic variables. Radial-velocity measurements gave an orbital period of ~1.345 hours, matching the radio burst cadence. The companion’s mass is ~0.096 M? and radius ~0.13 R?, consistent with an M6 red dwarf. These data provide the strongest direct link between an LPT and a white-dwarf binary.

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In a press release, the team announced the first definitive identification of an LPT source, noting that the white dwarf is actively drawing material from its companion. They emphasized that the orbital period’s match to the radio cadence offers compelling evidence for an accretion-driven emission mechanism.

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> “For the first time we have pinpointed the origin of these signals,” said Kovi Rose, a doctoral student at the University of Sydney’s School of Physics and the Commonwealth Scientific and Industrial Research Organisation. “We’ve been able to show that the source for one of these transients comes from a white dwarf actively pulling material from a companion star.” — Kovi Rose, Doctoral Student, University of Sydney

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The source appears under two catalog names—ASKAP J174508.9-505149 and ASKAP J1745-5051—within the same article, indicating a minor inconsistency.

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The identification supplies concrete evidence that some LPTs arise from magnetic cataclysmic variables. Confirming an accretion-driven origin resolves a long-standing ambiguity about the nature of these repeating radio bursts. It also demonstrates the value of wide-field radio surveys for discovering rare astrophysical sources.

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