Astronomers closer to deciphering the mysterious origin of fast radio bursts

Rapid radio burst reaching earth

Artist’s idea of ​​a rapid radio burst reaching Earth. Photo credit: Jingchuan Yu, Beijing Planetarium

New study by an international team of scientists identifies polarization as a key feature that could reveal the origin of powerful millisecond-long cosmic radio bursts.

Almost 15 years after the discovery of Fast Radio Bursts (FRBs), the origin of the millisecond-long cosmic explosions in space remains a mystery.

That could soon change, thanks to the work of an international team of scientists – including UNLV astrophysicist Bing Zhang – which tracked hundreds of outbursts from five different sources and found clues in FRB polarization patterns that could reveal their origin. The team’s findings were published in the March 17, 2022 issue of the journal science.

FRBs generate electromagnetic radio waves, which are essentially oscillations of electric and magnetic fields in space and time. The direction of the oscillating electric field is called the direction of polarization. By analyzing the polarization frequency in FRBs observed from different sources, scientists uncovered similarities in repetitive FRBs that indicate a complex environment near the source of the outbursts.

“This is an important step in understanding the physical origin of FRBs,” said Zhang, a distinguished professor of astrophysics at UNLV, who co-authored the paper and contributed to the theoretical interpretation of the phenomena.

To establish the link between the outbursts, an international team of researchers led by Yi Feng and Di Li of the National Astronomical Observatories of the Chinese Academy of Sciences analyzed the polarization properties of five repeating FRB sources using the massive 500-meter Aperture Spherical Radio Telescope (FAST) and the Robert C. Byrd Green Bank Telescope (GBT). Since the discovery of FRBs in 2007, astronomers worldwide have turned to powerful radio telescopes such as FAST and GBT to track the bursts, looking for clues as to where they are coming from and how they are produced.

Although still considered mysterious, it is widely believed that the source of most FRBs are magnetars, incredibly dense, city-sized neutron stars that possess the strongest magnetic fields in the universe. They typically have close to 100% polarization. Conversely, many astrophysical sources involving hot randomized plasmas, such as B. the Sun and other stars, the observed emission is unpolarized because the oscillating electric fields have random orientations.

This is where the cosmic detective work begins.

In a study the team originally published last year natureFAST detected 1,652 pulses from active repeater FRB 121102. Although the bursts from the source were highly polarized – consistent with magnetars – with other telescopes using higher frequencies, none of the bursts detected with FAST in its frequency band were polarized, although FAST was the largest single dish radio telescope in the world.

“We were very puzzled by the lack of polarization,” said Feng, first author of the newly released edition science Paper. “When we later systematically examined other repeating FRBs with other telescopes in different frequency bands – particularly those higher than FAST’s – a consistent picture emerged.”

According to Zhang, the unified picture is that each repeating FRB source is surrounded by a highly magnetized density[{” attribute=””>plasma. This plasma produces different rotation of the polarization angle as a function of frequency, and the received radio waves come from multiple paths due to scattering of the waves by the plasma. 

When the team accounted for just a single adjustable parameter, Zhang says, the multiple observations revealed a systematic frequency evolution, namely depolarization toward lower frequencies. 

“Such a simple explanation, with only one free parameter, could represent a major step toward a physical understanding of the origin of repeating FRBs,” he says. 

Di Li, a corresponding author of the study, agrees that the analysis could represent a corner piece in completing the cosmic puzzle of FRBs. “For example, the extremely active FRBs could be a distinct population,” he says. “Alternatively, we’re starting to see the evolutionary trend in FRBs, with more active sources in more complex environments being younger explosions.” 

The study, “Frequency-dependent polarization of repeating fast radio bursts—implications for their origin,” appeared March 17 in the journal Science. It includes 25 co-authors from 11 institutions and is part of long-running collaboration among institutions. In addition to UNLV and NAOC, collaborating institutions also include Yunnan University, Princeton University, Western Sidney University, Peking University and Green Bank Observatory, USA. 

Reference: “Frequency-dependent polarization of repeating fast radio bursts—implications for their origin” by Yi Feng, Di Li, Yuan-Pei Yang, Yongkun Zhang, Weiwei Zhu, Bing Zhang, Wenbin Lu, Pei Wang, Shi Dai, Ryan S. Lynch, Jumei Yao, Jinchen Jiang, Jiarui Niu, Dejiang Zhou, Heng Xu, Chenchen Miao, Chenhui Niu, Lingqi Meng, Lei Qian, Chao-Wei Tsai, Bojun Wang, Mengyao Xue, Youling Yue, Mao Yuan, Songbo Zhang and Lei Zhang, 17 March 2022, Science.
DOI: 10.1126/science.abl7759 Astronomers closer to deciphering the mysterious origin of fast radio bursts

Tom Vazquez

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