FAST observations reveal circular polarization in active repetitive Fast Radio Bursts

(ORDO NEWS) — A research team led by Professor Li Di of the National Astronomical Observatory of the Chinese Academy of Sciences has discovered circular polarization in active repetitive fast radio bursts.

The study used observations from the Five Hundred Meter Aperture Spherical Telescope (FAST).

Fast radio bursts (FRBs) are the brightest radio bursts in the universe. The calculated equivalent energy of a single FRB event can compete with the energy generated by the Sun over a full day.

Since the first FRB was reported in 2007, more than 600 sources of such bursts have been recorded, most of which were isolated. Less than 5% of all FRBs recur and less than 10 of them can be characterized as active.

Almost all repeating FRBs were found to have linear polarization. Circular polarization is relatively rare. Only one repeating circularly polarized FRB, FRB20201124A, has been reported.

FRB20121102A is the first known repeater. FRB20190520B, discovered by the Combensal Radio Astronomy FAST Survey (CRAFTS), is the first known permanently active repeater.

They are the only repeaters that are associated with constant radio sources, which may be a sign of their youth, and is due to their hyperactive nature.

FAST was able to capture extremely active episodes of these two FRBs, allowing for an accurate characterization of their polarization.

The researchers found circular polarization in less than 5% of the flares from both FRBs. The maximum degree of circular polarization was as much as 64%.

This work increases the number of known repeating circularly polarized FRBs from one to three.

The detection of circular polarization in FRB20121102A, 20190520B, and 20201124A may indicate that circular polarization is a common feature, albeit occurring sporadically, in repeating FRBs.

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