Repeating Fast Radio Burst Might Come From A Dancing Magnetosphere

Artistic view of LOFAR's so-called Superterp in Drenthe, the Netherlands, where low-frequency radio waves from the fast radio burst FRB20180916B were captured. Image Credit: Daniëlle Futselaa

Fast Radio Bursts (FRBs) are mysterious, powerful, and extremely brief emission of radio waves almost exclusively from beyond the Milky Way (here’s the exception). Some are believed to be associated with magnetars, extremely magnetic neutron stars, and several of them are known to repeat with regularity.

Among them, there’s FRB 180916. Scientists have witnessed the pattern of emission repeat every 16 days or so and believe that the emitting magnetar is orbiting another star or that it is spinning in a way that we are only getting the emission at regular intervals. Two new papers bring provide deeper observations of this particular cosmic phenomenon adding important new information but also raising more questions.

One of the papers is published in The Astrophysical Journal Letters. In this work, the team report on the emission of the FRB.  It is in burst mode for four days and then it is quiet for 12. FRBs are notorious for emitting high-frequency but the team employed the power of the Low-Frequency Array to study it with a broader spectrum. And they discover some barely detectable low-frequency emission delayed to about three days with respect to the burst.

"At different times we see radio bursts with different radio frequencies. Possibly the FRB is part of a binary star. If so, we would have a different view at different times of where these enormously powerful bursts are generated," co-author Jason Hessels, from the Netherlands Institute for Radio Astronomy ASTRON and the University of Amsterdam, said in a statement.

The scenario favored by these observations suggests the magnetar is orbiting and likely interacting with a high-mass stellar companion.

In the paper published in Nature Astronomy, the team looked at something called polarization of the radio waves. Light is made of electromagnetic waves that oscillate on planes that are perpendicular to the direction of travel. Usually, the orientations of those planes are random. But in astronomical settings (or purposefully in 3D cinema) light becomes polarized, so it oscillates in special planes.

Astronomers have found highly polarized microstructure lasting a few microseconds within the burst, which in turn last just milliseconds. The team believes that the explanation for this is that the magnetosphere of this neutron star is dancing as it interacts with its companion.

More observations probing these and lower frequencies are planned to probe this extraordinary system even further. FRB 180916 is emitted from a galaxy 500 million light-years away.

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