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Fast Radio Bursts, or FRBs, powerful millisecond-long radio waves coming from deep space outside the Milky Way, are among the most mysterious astronomical phenomena ever observed. Since FRBs were first discovered in 2007, astronomers around the world have used radio telescopes to track the bursts and look for clues about where they come from and how they are produced.
UNLV astrophysicist Bing Zhang and international collaborators recently looked at some of these mysterious sources, leading to a series of important discoveries published in the journal Nature that may finally shed light on the physical mechanism of FRBs.
The first article, of which Zhang is a corresponding author and leading theorist, was published in the October 28, Nature.
“There are two main questions about the origin of FRBs,” said Zhang, whose team made the observation using the Five-Hundred Aperture Spherical Telescope (FAST) in Guizhou, China. “The first is what are the FRB motors and the second is what is the mechanism for producing FRBs. We found the answer to the second question in this document.”
Two competing theories have been proposed to interpret the mechanism of FRBs. One theory is that they are similar to gamma ray bursts (GRBs), the most powerful bursts in the universe. The other theory compares them more to radio pulsars, which are rotating neutron stars that emit bright, coherent radio pulses. GRB-like models predict a non-variable polarization angle within each burst, while pulsar-like models predict polarization angle variations.
The team used FAST to observe a repeating FRB source and discovered 11 bursts of it. Surprisingly, seven of the 11 bright bursts showed various polarization angle changes during each burst. Not only did the polarization angles vary with each burst, the patterns of variation were also diverse between bursts.
“Our observations essentially rule out GRB-like models and offer support for pulsar-like models,” said K.-J. Lee of the Kavli Institute for Astronomy and Astrophysics at Peking University and corresponding author of the paper.
Four other articles on FRB were published in Nature on November 4. These include several research papers published by the FAST team led by Zhang and collaborators from the National Astronomical Observatories of China and Peking University. Researchers affiliated with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Survey group for Transient Astronomical Radio Emissions 2 (STARE2) also joined in the publications.
“Just as the first article advanced our understanding of the mechanism behind FRBs, these articles solved the challenge of their mysterious origin,” Zhang explained.
Magnetars are incredibly dense city-sized neutron stars that possess the most powerful magnetic fields in the universe. Magnetars occasionally produce short X-rays or soft gamma-ray bursts through the dissipation of magnetic fields, which is why they have long been speculated as plausible sources to power FRBs during high-energy bursts.
The first conclusive evidence for this came on April 28, 2020, when an extremely bright radio burst was detected from a magnetar located right in our backyard, at a distance of approximately 30,000 light years from Earth in the Milky Way. Unsurprisingly, the FRB was associated with a bright X-ray burst.
“We now know that the most magnetized objects in the universe, the so-called magnetars, can produce at least some or possibly all of the FRBs in the universe,” Zhang said.
The event was detected by CHIME and STARE2, two sets of telescopes with many small radio telescopes that are suitable for detecting bright events over a large area of the sky.
Zhang’s team has been using FAST to observe the source of the magnetar for some time. Unfortunately, when the FRB occurred, FAST was not looking at the source. Nonetheless, FAST made some intriguing “no detection” discoveries and reported them in one of the November 4 reports. Nature articles. During the FAST observation campaign, there were another 29 X-ray bursts emitted by the magnetar. However, none of these bursts were accompanied by a radio burst.
“Our non-detections and the detections from the CHIME and STARE2 teams paint a complete picture of the FRB-magnetar associations,” Zhang said.
To put everything in perspective, Zhang also worked with Nature to publish a single-author review of the various discoveries and their implications for the field of astronomy.
“Thanks to recent advances in observation, FRB theories can finally be critically reviewed,” Zhang said. “FRB production mechanisms have been greatly reduced. However, many open questions remain. This will be an exciting field in the years to come.”
