International Team of Astronomers Reports on Largest-ever Observed Set of Mysterious Fast Radio Bursts

Reported by Tony Allen in UNLV News Center.

An international team of astronomers recently observed more than 1,650 fast radio bursts (FRBs) detected from one source in deep space, which amounts to the largest set – by far – of the mysterious phenomena ever recorded.

More than a decade after the discovery of FRBs, astronomers are still baffled by the origins of the millisecond-long, cosmic explosions that each produce the energy equivalent to the sun’s annual output.

In a study published in the Oct. 13 issue of the journal Nature, scientists – including UNLV astrophysicist Bing Zhang – report on the discovery of a total of 1,652 independent FRBs from one source over the course of 47 days in 2019. The source, dubbed FRB 121102, was observed using the Five-hundred-meter Aperture Spherical Telescope (FAST) in China, and represents more FRBs in one event than all previous reported occurrences combined.

“This was the first time that one FRB source was studied in such great detail,” said Zhang, one of the study’s corresponding authors. “The large burst set helped our team hone in like never before on the characteristic energy and energy distribution of FRBs, which sheds new light on the engine that powers these mysterious phenomena.”

Since FRBs were first discovered in 2007, astronomers worldwide have turned to powerful radio telescopes like FAST to trace the bursts and to look for clues on where they come from and how they’re produced. The source that powers most FRBs is widely believed to be magnetars, incredibly dense, city-sized neutron stars that possess the strongest magnetic fields in the universe. And while scientists are gaining greater clarity on what produces FRBs, the exact location of where they occur is still a mystery.

A mystery that recent results may be starting to unravel.

According to Zhang, there are two active models for where FRBs come from. One could be that they come from magnetospheres, or within a magnetar’s strong magnetic field. Another theory is that FRBs form from relativistic shocks outside the magnetosphere traveling at the speed of light.

“These results pose great challenges to the latter model,” says Zhang. “The bursts are too frequent and - given that this episode alone amounts to 3.8% of the energy available from a magnetar - it adds up to too much energy for the second model to work.”

The bursts were measured by FAST within a total of 59.5 hours over 47 days from Aug. 29 to Oct. 29, 2019. 

“During its most active phase, FRB 121102 included 122 bursts measured within a one-hour period, the highest repeat rate ever observed for any FRB,” said Pei Wang, one of the article’s lead authors from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).

Researchers expect that FAST will continue to systematically investigate a large number of repeating FRBs in the future.

“As the world’s largest antenna, FAST’s sensitivity proves to be conducive to revealing intricacies of cosmic transients, including FRBs,” said Di Li, the study’s lead researcher from NAOC.

The study includes more than 30 co-authors from 16 institutions in four countries and is part of a long-running collaboration among the institutions. In addition to UNLV and NAOC, collaborating institutions include Guizhou Normal University, Cornell University, Max Planck Institute for Radio Astronomy, West Virginia University, CSIRO Astronomy and Space Science, University of California Berkeley, and Nanjing University.

Publication Details: “A bimodal burst energy distribution of a repeating fast radio burst source,” was published in the Oct. 13, 2021 issue of the journal Nature.

Professor Monika Mościbrodzka. Imaging Magnetic Fields at the Edge of M87's Black Hole. Thursday April 29, 2021 at 7PM PDT (ONLINE).

The Russell Frank Astronomy Lecture Series
UNLV Physics and Astronomy Department
7:00PM PDT Thursday April 29, 2021
2:00AM GMT Friday April 30, 2021
Webex link https://unlv.webex.com/unlv/j.php??MTID=m9b77c4799c5efce726b9afdbd984e08a

Two years ago, scientists presented the first image of a black hole at the center of a galaxy. We see a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. Last month, for the first time, observations revealed the signature of magnetic fields close to the edge of a black hole. These new images are the key to explaining how the black hole is able to launch energetic jets. Dr. Mościbrodzka will discuss how these images of the black hole were made and their meaning.

This talk is intended for a general audience including enthusiasts of all backgrounds and ages.

Bing Zhang contributes to understanding the physical mechanisms of fast radio bursts in three papers published in Nature.

Authored by Shane Bevell for the UNLV News Center, November 4, 2020.

Fast radio bursts, or FRBs – powerful, millisecond-duration radio waves coming from deep space outside the Milky Way Galaxy – have been among the most mysterious astronomical phenomena ever observed. Since FRBs were first discovered in 2007, astronomers from around the world have used radio telescopes to trace the bursts and look for clues on where they come from and how they’re produced.

UNLV astrophysicist Bing Zhang and international collaborators recently observed some of these mysterious sources, which led to a series of breakthrough discoveries reported in the journal Nature that may finally shed light into the physical mechanism of FRBs.

The first paper, for which Zhang is a corresponding author and leading theorist, was published in the Oct. 28 issue of Nature.

“There are two main questions regarding the origin of FRBs,” said Zhang, whose team made the observation using the Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou, China. “The first is what are the engines of FRBs and the second is what is the mechanism to produce FRBs. We found the answer to the second question in this paper.”

Two competing theories have been proposed to interpret the mechanism of FRBs. One theory is that they’re similar to gamma-ray bursts (GRBs), the most powerful explosions in the universe. The other theory likens them more to radio pulsars, which are spinning neutron stars that emit bright, coherent radio pulses. The GRB-like models predict a non-varying polarization angle within each burst whereas the pulsar-like models predict variations of the polarization angle.

The team used FAST to observe one repeating FRB source and discovered 11 bursts from it. Surprisingly, seven of the 11 bright bursts showed diverse polarization angle swings during each burst. The polarization angles not only varied in each burst, the variation patterns were also diverse among bursts.

“Our observations essentially rules out the GRB-like models and offers support to the pulsar-like models,” said K.-J. Lee from the Kavli Institute for Astronomy and Astrophysics, Peking University, and corresponding author of the paper.

Four other papers on FRBs were published in Nature on Nov. 4. These include multiple research articles 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 for Transient Astronomical Radio Emission 2 (STARE2) group also partnered on the publications.

“Much like the first paper advanced our understanding of the mechanism behind FRBs, these papers solved the challenge of their mysterious origin,” explained Zhang.

Magnetars are incredibly dense, city-sized neutron stars that possess the most powerful magnetic fields in the universe. Magnetars occasionally make short X-ray or soft gamma-ray bursts through dissipation of magnetic fields, so they have been long speculated as plausible sources to power FRBs during high-energy bursts.

The first conclusive evidence of this came on April 28, 2020, when an extremely bright radio burst was detected from a magnetar sitting right in our backyard – at a distance of about 30,000 light years from Earth in the Milky Way Galaxy. As expected, 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 FRBs in the universe,” said Zhang.

The event was detected by CHIME and STARE2, two telescope arrays with many small radio telescopes that are suitable for detecting bright events from a large area of the sky.

Zhang’s team has been using FAST to observe the magnetar source for some time. Unfortunately, when the FRB occurred, FAST was not looking at the source. Nonetheless, FAST made some intriguing “non-detection” discoveries and reported them in one of the Nov. 4 Nature articles. During the FAST observational campaign, there were another 29 X-ray bursts emitted from the magnetar. However, none of these bursts were accompanied by a radio burst.

“Our non-detections and the detections by the CHIME and STARE2 teams delineate a complete picture of FRB-magnetar associations,” Zhang said.

To put it all into 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 observational breakthroughs, the FRB theories can finally be reviewed critically,” said Zhang. “The mechanisms of producing FRBs are greatly narrowed down. Yet, many open questions remain. This will be an exciting field in the years to come.”

Read More

• "No pulsed radio emission during a bursting phase of a Galactic magnetar," published in the Nov. 4 issue of Nature.
• "The physical mechanisms of fast radio bursts," published in the Nov. 4 issue of Nature.
• "Diverse polarization angle swings from a repeating fast radio burst source," published in the Oct. 28 issue of Nature.