Â鶹ÒùÔº

New long-period radio transient discovered

An international team of astronomers reports the discovery of a new long-period radio transient, which received the designation ASKAP J144834−685644 (ASKAP J1448−6856 for short). The newfound transient is a crucial addition to the still short list of sources of this type. The finding was detailed in a paper July 17 on the arXiv preprint pre-print server.

Long-period radio transients (LPTs) are an emerging class of periodic radio emitters, with ultralong rotation periods (ranging from minutes to hours) and strong magnetic fields. Although some observations have suggested that these transients may originate from rotating neutron stars with extremely strong magnetic fields (magnetars) or magnetic white dwarfs, their true nature still baffles astronomers.

The Australian Square Kilometre Array Pathfinder (ASKAP) is a 36-dish radio-interferometer in Australia, operating at 700 to 1,800 MHz. One of its scientific goals is the characterization of radio transient sky through the detection and monitoring of transient and variable sources.

Now, a group of astronomers led by Akash Anumarlapudi of the University of Wisconsin–Milwaukee reports the newest detection with ASKAP. By conducting a search for circularly polarized sources, they identified one that shows highly variable linearly and circularly polarized emission.

"We report the discovery of a new LPT, ASKAP J1448−6856. Discovered as a 1.5-hour periodic radio source, ASKAP J1448−6856, shows a steep spectrum, elliptical polarization, and periodic narrowband emission that declines at frequencies above 1.5 GHz," the researchers wrote in the paper.

The newfound LPT exhibits emission with a harmonic frequency structure, and polarized bursts. Its emission is elliptically polarized, with the polarization fraction varying from 35 to 100% between observations.

The astronomers underlined that unlike most other LPTs, ASKAP J1448−6856 is detected across wavelengths from X-rays to radio, and shows variability at optical bands. This makes it one of the very few LPTs that has been identified from X-rays to radio wavelengths.

According to the paper, multiwavelength modeling of the spectral energy distribution (SED) of ASKAP J1448−6856, combined with its radio properties, suggest that it may be a near-edge-on magnetic white dwarf (MWD) binary system with a magnetic field strength of over 1,000 Gauss.

However, the authors of the study do not exclude the possibility that ASKAP J1448−6856 may be an isolated white dwarf pulsar or a transitional millisecond pulsar-like system.

Summing up the results, the scientists noted how important the discovery of ASKAP J1448−6856 is in advancing our understanding of the LPT population.

"Combining ASKAP J1448−6856 with the growing number of long-period radio transients adds to the variety of multi-wavelength behavior and will help deepen our understanding of this emerging population (or, indeed, populations)," the astronomers concluded.