The discovery of FRB 20190520B, the world’s first persistently active repeating FRB, is attributed to the Commensal Radio Astronomy FAST Survey (CRAFTS), a vital initiative of the Five-hundred-meter Spherical radio Telescope (FAST). This FRB has provided some insights that may help in the understanding of the origin of FRBs.
Under the leadership of Dr. LI Di from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), an international team conducted a monitoring campaign of FRB 20190520B, using the Parkes telescope in Australia and the Green Bank Telescope (GBT) in the United States. The combined analyses have revealed an extreme field reversal around this constantly bursting source.
Unlike other FRBs, FRB 20190520B is known to produce bursts detectable by at least one, and sometimes multiple telescopes, every time it is viewed, making it an ideal target for multiband follow-up observational studies.
In a recent study, Dr. FENG Yi and Ms. Anna-Thomas utilized data from GBT and Parkes to analyze the polarization properties of a burst signal, ultimately measuring its Faraday rotation measure (RM). They discovered that the RM experienced a striking sign change twice, going from approximately 10,000 units to -10,000 units and back again. Key contributors to this study include Dr. Liam Connor from Caltech and Dr. Sarah Burke-Spolaor from WVU.
The surrounding plasma can affect the polarization characteristics of a burst signal as it propagates. According to the study’s corresponding author, Dr. LI Di, this change in RM occurs due to a reversal of magnetic fields, as electron density cannot go negative. This reversal could be caused by a turbulent, magnetized screen of plasma located between 10-5 to 100 parsecs of the FRB source. Prof. YANG Yuanpei, a co-author of the study, likens the turbulent magnetic field components around repeating fast radio bursts to a messy ball of wool.
The most likely explanation for this chaotic environment includes the signal passing through the halo of a companion, which could be a blackhole or a massive star with winds. Understanding the magnetized environment around FRBs is an essential step in comprehending the origin of these cosmic explosions.
