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Deep Mining of China's FAST Observation Data | the Latest Results of Computational Astronomy Were Published on the Cover of Science Bulletin
Date: 2023-01-01

On December 26, FENG Yi, research expert at the Research Center for Intelligent Computing Platforms of Zhejiang Lab, and other researchers published their latest research results in the cover article of the Science Bulletin, a comprehensive leading journal of the "China Science and Technology Journal Excellence Action Plan". Relying on the intelligent computing astronomy platform jointly built by Zhejiang Lab and the National Astronomical Observatories, CAS, the results, which is based on the FRB and pulsar search and exploration model and astronomical data processing model, utilize intelligent computing technologies such as data mining, machine learning and advanced computing to conduct in-depth mining of the data of China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST).

In this study, Dr. FENG Yi, the first author, and Dr. ZHANG Yongkun from the National Astronomical Observatories, CAS, systematically analyzed the observation data of FAST. Circular polarization had been successfully measured in FRB20121102A and FRB20190520B, two FRBs with repetitive bursts, increasing the number of the repetitive burst sample from one to three.

"The discovery finely describes the polarization characteristics of this mysterious phenomenon in the dynamic universe, suggesting that a small amount of circular polarization may be a common feature of active repetitive FRBs", said Researcher LI Di, the corresponding author as well as ZJ Lab's Chief Computational Astronomer of Data Reactor and Chief Scientist at the National Astronomical Observatories, CAS.

FRB is the most intense burst of radio waves in the universe that can emit energy in a few thousandths of a second equal to that the sun does in a day, a month or even a year. The corresponding radiation mechanism and origin are not yet known. So far, more than 600 FRBs have been detected, the vast majority of which have only been detected once, and less than 5% of FRBs have been observed to burst repetitively. Of the more than 600 reported FRBs, there are only two extremely active repetitive bursts, i.e. FRB20121102A and FRB20190520B, which have corresponding persistent radio sources (PRS). This may indicate their particular origin or represent a young stage in the evolution of FRBs.

As one of the basic properties of electromagnetic waves, polarization carries the intrinsic radiation characteristics of light source and the key information of light propagation environment. Linear polarization has been detected in almost all repetitive FRBs, but circular polarization is rare, which has only been reported in FRB20201124A.

Through in-depth monitoring, China's FAST captured the extremely active phases of FRB20121102A and 20190520B, which accumulated a large amount of valuable observation data and enabled researchers to finely characterize their polarization characteristics.

Twelve polarization profiles (A01-12) of FRB 20121102 and three polarization profiles (B01–03) of FRB 20190520B have circular polarization bursts. Black, red, and blue lines represent total intensity, linear polarization, and circular polarization, respectively.

FENG Yi and ZHANG Yongkun systematically analyzed the data set of FAST and found that less than 5% of bursts have the characteristics of circular polarization radiation, but the ratio of circular polarization is up to 64%. Such a high ratio limits the possibility that circular polarization comes from multipath propagation. Possible mechanisms include Faraday conversion in extreme magnetic field environments or intrinsic characteristics of FRB sources. Based on previous calculations, circular polarization is more likely to occur in non-repetitive FRBs than in repetitive bursts. Under either mechanism, the conditions for circular polarization of repetitive bursts are more stringent.

Further systematic and detailed characterization of the RF polarization characteristics of the dynamic universe by FAST will deepen the understanding of the radiation mechanism of FRBs, which is expected to eventually reveal the origin of this mysterious astrophysical phenomenon.