Twisted Fields Discovered Around Mysterious Fast Radio Burst

An international team of researchers led by Dr LI Di, of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), has carried out a monitoring campaign for FRB 20190520B, using the Parkes telescope in Australia and the Green Bank Telescope (GBT), in the United States, and the combined analyzes have revealed an extreme inversion of the field around this constantly bursting source, as published in the journal ‘Science’. Fast Radio Bursts (FRBs) are the brightest millisecond-long cosmic explosions in radio bands. Its unknown origin poses challenges for both astronomy and physics.

The Commensal Radio Astronomy FAST Survey (CRAFTS), a key program of the Five Hundred Meter Spherical Radio Telescope (FAST), discovered the world’s first persistently active repeating FRB, known as FRB 20190520B. Now, this FRB has provided clues that can help clarify the origin of the FRBs.

Unlike all other FRBs, FRB 20190520B has produced outbursts, detectable by at least one and sometimes multiple telescopes, every time it has been observed. This reliability makes it an ideal target for multiband follow-up observational studies. “A total of 113 outbursts from FRB 20190520B were detected by the Parkes telescope, exceeding the sum of the number of fast radio outbursts previously discovered in Parkes, accentuating the value of FRB 20190520B,” explains Dr. DAI Shi from the University of Western Sydney, PI of the FRB 20190520B project in Parkes.

Through a combined analysis of the GBT and Parkes data, Dr. FENG Yi, an NAOC PhD graduate now in the Zhejiang Laboratory, and Anna-Thomas of West Virginia University (WVU) measured its polarization properties. and found that the Faraday rotation (RM) measure changed its sign dramatically twice: from about 10,000 units to about 10,000 units and vice versa. During the propagation of a burst signal, the polarization characteristics can be affected by the surrounding plasma. “The RM can be approximated by the integral product of the magnetic field and the electron density. The variation of the MR can be due to either of the two factors, but the change of sign has to arise from the reversal of the magnetic fields, since the electron density cannot become negative,” explains LI Di, Ph.D., corresponding author of the study.

This reversal could be due to propagation through a turbulent, magnetized plasma screen located between 10-5 and 100 parsecs from the FRB source. “The turbulent components of the magnetic field around repeated fast radio bursts can be as messy as a ball of wool,” says Professor YANG Yuanpei of the University of Yunnan, a co-author of the study.

source: An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102. Nature553, 182–185 (2018).