First fast radio burst with a reversible magnetic field discovered

A phenomenon never before seen has just been observed around a fast radio burst by an international team of researchers.

Fast radio bursts (FRBs) are among the most mysterious objects in our universe. They are known only from the brief, intense flashes of radio frequency radiation that they shoot across the cosmos.

Observations of a repeating FRB, called 20190520B, have revealed that the dense plasma surrounding the radio source is highly magnetised and  very turbulent. Over the course of 17 months of observations, the direction of the magnetic field in the plasma changed twice – something never seen around an FRB before.

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The researchers used data on FRB 20190520B from the ultra-wideband receiver on the CSIRO’s Parkes radio telescope, Muriyang in the Australian state of New South Wales, and the Green Bank Telescope in Virginia, US.

FRBs were first discovered in 2007 using the Parkes telescope. Since then, astronomers have racked their brains over these enigmatic objects. Despite extensive research, the origin of FRBs remain a mystery.

“We know that FRBs originate from sources in distant galaxies,” says Dr Shi Dai, an from Western Sydney University (WSU), and lead co-author on a paper published in Science on the latest observations.

“This makes FRBs unique tools to probe a range of astrophysics, such as “missing” matter in between galaxies, the expansion of the Universe, and astrophysics in dense and highly magnetised environments.”

FRB 20190520B was first detected in 2019 using data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China. Its discovery was announced in 2022.

As reported on Cosmos last year, the FRB is located in a dwarf galaxy known as J160204.31−111718.5 about 3 billion light years from Earth. FRB 20190520B is one of a rare class of FRB found to repeat its radio bursts.

Over the course of the study, the team detected more than 100 bursts from FRB 20190520B. Of these bursts, 13 exhibited polarised emission, indicating a magnetic field. And the magnetic field twice changed direction.

“The change of the direction of the magnetic field put some strong constraints on the origin of this FRB,” says co-author, WSU’s Professor Miroslav Filipovic. “It requires that the source of FRB is moving relative to a large-scale magnetic field.”

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“One of the possibilities that we proposed is that the FRB source is a binary system with a star, which has strong stellar wind with a strong magnetic field. As the FRB source orbits the star, it moves in and out from the wind, which can explain our observations.”

“The binary-system model for FRBs can be tested with future observations since we expect the observational features to repeat periodically if the source really is in a binary system,” adds Dr Shi Di.

“Our work delivered one of the clearest pictures of the source of fast radio bursts, which will have profound implications on our understanding of FRBs and their origin.”

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