An international team of researchers has unlocked the latest clue in the search for what drives some fast radio bursts (FRBs) – violent, deep-space cosmic explosions of electromagnetic radiation that in just milliseconds produce the energy equivalent of our sun’s annual output.
First discovered just over a decade ago, FRBs remain among the most mysterious events in the universe. Despite extensive research, the precise mechanisms driving these bursts remain unclear. However, in a few instances, the brief flash of an FRB is accompanied by a weaker, persistent radio emission.
A new study led by the Italian National Institute for Astrophysics (INAF) and an international team of scientists – including UNLV astrophysicist Bing Zhang – has revealed that the persistent emission of radiation following the initial flash of some FRBs is likely generated by plasma bubbles. The study was published Aug. 7 in the journal Nature.
Researchers focused on FRB20201124A, a fast radio burst discovered in 2020 whose source is located about 1.3 billion light-years away from Earth. The FRB was captured in observations by the Karl G. Jansky Very Large Array (VLA) in New Mexico, which is currently the most sensitive radio telescope in the world, along with other arrays worldwide. This combination of sources allowed scientists to build a comprehensive picture of the FRB and its host galaxy.
“We were able to demonstrate through observations that the persistent emission observed along with some fast radio bursts behaves as expected from the nebular emission model, i.e. a ‘bubble’ of ionized gas that surrounds the central engine,” explains Gabriele Bruni, INAF researcher and lead author of the new paper. “Through radio observations of one of the bursts that is nearest to us, we were able to measure the weak persistent emission coming from the same location as the FRB, extending the radio flux range explored so far for these objects by two orders of magnitude."
These observations suggest that the central engines of these FRBs could be magnetars, incredibly dense, city-sized neutron stars that possess the most powerful magnetic fields in the universe. Because magnetars occasionally produce X-ray bursts through dissipation of magnetic fields, they’re viewed as plausible sources to power FRBs. Another possibility is that they are driven by what are known as high-accretion X-ray binary systems, which consist of a neutron star or black hole and draw in material from companion stars at very high rates.
According to researchers, winds produced by a magnetar or X-ray binary would be able to “blow” the plasma bubble that leads to the persistent radio emission.
“According to our theory, the brightness of persistent radio sources should linearly scale with the Faraday rotation measure, a parameter that measures the strength and density of the medium surrounding the FRB source,” said Bing Zhang, study co-author and professor and director of the Nevada Center for Astrophysics at UNLV. “What we’ve observed aligns very well with prediction models, suggesting a consistent picture of known FRB sources.”
Though most FRBs do not exhibit a measurable persistent emission, researchers say that understanding the nature of the emission offers is crucial to solving the puzzle about the origins of these mysterious cosmic sources.
“Persistent radio sources from most FRBs are predicted to be too faint to detect, which is consistent with our theory,” said Zhang. “Detecting more radio bubbles around nearby FRBs with more magnetized environments will further test our theory and bring us another step closer to understanding the nature and origin of FRBs.”
Publication Details
The study, “A nebular origin for the persistent radio emission of fast radio bursts,” was published Aug. 7 in the journal Nature. Along with INAF and UNLV researchers, the collaboration involves the Universities of Bologna, Trieste and Calabria, in Italy, and the international participation of research institutes and universities in the U.S., China, Spain, and Germany.
