Long-period radio transients (LPTs) are an emerging group of radio transients that show periodic polarised 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 remains unclear. The first example of an LPT to be detected at both radio and X-ray energies was reported just last month. Now, Anumarlapudi et al. report the discovery of a new 1.5 hr LPT, ASKAP J144834−685644, which has also been detected at radio and X-rays. It shows a steep radio spectrum and polarised radio bursts, which resemble the radio emission in known LPTs. In addition, it also shows highly structured and periodic narrow-band radio emission. Multi-wavelength properties suggest that the spectral energy distribution (SED) peaks at near ultraviolet wavelengths, indicating the presence of a hot magnetic source. Combining multi-wavelength information, they infer that ASKAP J144834−685644 may be a near edge-on magnetic white dwarf binary (MWD), although they cannot fully rule out ASKAP J144834−685644 being an isolated white dwarf pulsar or even a transitional millisecond pulsar. If ASKAP J144834−685644 is a MWD binary, the observed broadband spectral energy distribution can be explained by emission from an accretion disk. This hints that some fraction of optically bright LPTs may be accreting binaries with the radio period being the orbital period.

The image above shows dynamic spectra of all four Stokes parameters with a 10-second time resolution and 1-MHz frequency resolution from a 10 hr ASKAP EMU observation on 15 June 2023, with a 799–1090 MHz bandpass. Multiple radio bursts can be seen in all four polarisations. The colour scale on the right represents the flux density. The horizontal gaps (white lines) in the spectra are the flagged frequency channels. The two persistent narrow-band features (around 900 and 950 MHz) are likely due to un-flagged radio frequency interference (RFI).