Astronomers discover a warped field around a mysterious fast radio burst

May 12, 2023

(Nanowerk News) Fast Radio Bursts (FRBs), characterized as the brightest millisecond-long sky bursts in the radio spectrum, have long posed puzzling questions to the world of astronomy and physics due to their enigmatic origins.

The Commensal Radio Astronomy FAST Survey (CRAFTS), a seminal program of the Five hundred meter Spherical Radio Telescope (FAST), has made a groundbreaking discovery: the first continuously active repeating FRB, designated FRB 20190520B. This unique FRB has shed light on potential clues that could explain the origin of this phenomenon.

An international consortium, spearheaded by Dr. LI Di of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), conducted the FRB 20190520B observation campaign. This effort, leveraging the capabilities of the Parkes telescope in Australia and the Green Bank Telescope (GBT) in the United States, uncovered extreme magnetic field reversals around this perpetually exploding source.

This multinational collaborative research effort is featured in Science (“Reversal of the magnetic field in a turbulent environment around repeated fast radio bursts”). Rotate the field around a mysterious fast radio burst. (Image LI Di/ScienceApe/CAS) (click on image to enlarge)

Unlike its counterparts, FRB 20190520B uniquely produces bursts that can always be detected by at least one, and often several, telescopes during each observation. This unfailing repeatability makes it an optimal candidate for a comprehensive multiband follow-up study.

“A total of 113 bursts from FRB 20190520B detected by the Parkes telescope, surpassing the cumulative number of fast radio bursts previously discovered at Parkes, thereby underscoring the extraordinary importance of FRB 20190520B,” said Dr. DAI Shi of Western Sydney University, Principal Investigator of project FRB 20190520B at Parkes.

Through a combined analysis of data collected from GBT and Parkes, Dr. FENG Yi, a NAOC alumnus now in the Zhejiang Laboratory, and Ms. Anna-Thomas of the University of West Virginia (WVU), measured its polarization attribute. They found that the Faraday rotation measure (RM) undergoes a radical sign shift: it oscillates from about 10,000 units to -10,000 units, and reciprocally. Other important contributors include Dr. Liam Connor of Caltech and Dr. Sarah Burke-Spolaor of WVU.

During the trajectory of the burst signal, the polarization properties can be affected by the enveloping plasma. “The RM can be approximated by the integral product of the magnetic field and the electron density. Although fluctuations in the RM can be caused by either factor, the change in sign must come from a reversal of the magnetic field, because the electron density cannot assume a negative value,” explained Dr. LI Di, corresponding study author.

This reversal may be a consequence of the signal traversing a magnetically turbulent plasma screen located within 10-5 up to 100 parsecs from source FRB. “The turbulent component of the magnetic field surrounding the repeated fast radio bursts might resemble a chaotic ball of wool,” argues Prof. YANG Yuanpei of Yunnan University, one of the study’s authors.

A plausible explanation for this chaos could be a signal crossing the halo of a companion entity, such as a black hole or a massive wind-driven star. Gaining insight into severe changes in the magnetic environment around these FRBs is an important step towards understanding the origins of these cosmic explosions.

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