Fast radio bursts (FRBs) are extremely powerful but incredibly brief flashes of radio waves coming from distant galaxies and lasting just milliseconds. As a general class, they are very puzzling to astronomers. Some repeat, others do not. Some seem to be from a clear type of source, others could be explained by many different events. There is still a lot to know about FRBs, and a never-before-seen behavior has just been added to the list.
The source in question is FRB 20190520B, a repeating FRB discovered on May 20, 2019. Astronomers followed the source for 17 months and measured 138 bursts using two observatories: the Green Bank Telescope in West Virginia and CSIRO’s Parkes Radio Telescope, Murriyang in Australia. Thirteen of those bursts were polarized – when the light that is made oscillates in a specific direction – and these offered incredible insights into the system.
Polarization can be used to study magnetic fields. For the first time, researchers found that the magnetic field around this FRB source changes direction twice over a short period of time. They also found that the environment of this source is dense plasma, both highly magnetized and highly turbulent – an indication that this FRB is orbiting a stellar companion releasing a lot of stellar wind.
"The change of the direction of the magnetic field put some strong constraints on the origin of this FRB. It requires that the source of FRB is moving relative to a large-scale magnetic field,” co-author Professor Miroslav Filipovic, from Western Sydney University, said in a statement.
“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."
Other repeating FRB sources are believed to orbit stellar companions. It is believed they are highly magnetic neutron stars and that their orbital motion leads to the periodical release of FRBs. But there is so much more that we need to understand about them.
“We know that FRBs originate from sources in distant galaxies. 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,” said co-author Dr Shi Dai, also from Western Sydney University,
“FRB 20190520B is one of a rare class of FRBs found to repeat. FRB 20190520B, first discovered by the FAST telescope in a survey led by Dr Di Li, is not only active but more importantly can be detected over a wide radio frequency window, which enables us to use the most advanced radio instruments, such as Parkes and its ultra-wideband receiver, to carry out detailed studies.”
The team will continue to follow up on this source to expand our knowledge of FRBs.
The study is published in the journal Science.