ASKAP J144834-685644: a newly discovered long period radio transient detected from radio to X-rays

TL;DR

This paper reports the discovery of ASKAP J144834-685644, a long-period radio transient detected across radio to X-ray wavelengths, likely representing a magnetic white dwarf binary with implications for understanding similar transient sources.

Contribution

The discovery of ASKAP J144834-685644 as a long-period radio transient detected from radio to X-ray wavelengths, suggesting a new class of accreting binary systems or white dwarf pulsars.

Findings

Detected a 1.5-hour long-period radio transient with polarized bursts.

Multiwavelength data suggest a magnetic white dwarf binary origin.

Broadband SED peaks at near-ultraviolet wavelengths.

Abstract

Long-period radio transients (LPTs) are an emerging group of radio transients that show periodic polarized radio bursts with periods varying from a few minutes to a few hours. Fewer than a dozen LPTs have been detected so far, and their origin (source and emission mechanism) remains unclear. Here, we report the discovery of a 1.5 h LPT, ASKAP J144834-685644, adding to the current sample of sources. ASKAP J144834-685644 is one of the very few LPTs that has been detected from X-rays to radio. It shows a steep radio spectrum and polarized radio bursts, which resemble the radio emission in known LPTs. In addition, it also shows highly structured and periodic narrow-band radio emission. Multiwavelength properties suggest that the spectral energy distribution (SED) peaks at near ultraviolet wavelengths, indicating the presence of a hot magnetic source. Combining multiwavelength information, we infer that ASKAP J144834-685644 may be a near edge-on magnetic white dwarf binary (MWD), although we cannot fully rule out ASKAP J144834-685644 being an isolated white dwarf pulsar or even a transitional millisecond pulsar (despite the lack of radio pulsations). If ASKAP J144834-685644 is a MWD binary, the observed broad-band SED can be explained by emission from an accretion disc. This hints that some fraction of optically bright LPTs may be accreting binaries with the radio period being the orbital period. It might further suggest a connection between optically bright synchronized WD binaries, such as polars, and non-accreting asynchronous WD pulsars, such as AR Sco and J1912-4410.