CHIME/Dunlap Institute
Astronomers have been concerned about the origins of mysterious fast radio bursts (FRBs) since the first one was spotted in 2007. Researchers are now looking for the first time at non-repeating FRBs, that is, those that have so far produced only a single burst of light. have produced. The authors of a new paper published in The Astrophysical Journal looked specifically at the properties of polarized light emitted by these FRBs, providing further insight into the origins of the phenomenon. The analysis supports the hypothesis that there are different origins for repetitive and non-repetitive FRBs.
“This is a new way to analyze the data we have on FRBs. Instead of just looking at how bright something is, we also look at the angle of the vibrating electromagnetic waves of light,” said co-author Ayush Pandhi, a graduate student at the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics. “It gives you additional information about how and where that light is produced and what it has experienced on its journey to us over many millions of light years.”
As we previously reported, FRBs involve a sudden burst of radio frequency radiation that lasts only a few microseconds. Astronomers have more than a thousand so far; some come from sources that repeatedly emit FRBs, while others appear to burst once and go silent. You can produce these kinds of sudden energy flows by destroying something. But the existence of repeating sources suggests that at least some of them were produced by an object that survives the event. That has led to a focus on compact objects such as neutron stars and black holes – especially a class of neutron stars called magnetars – as likely sources.
Many FRBs have also been detected that do not appear to repeat at all, suggesting that the conditions that spawned them may destroy their source. That’s equivalent to a blitzar – a bizarre astronomical event caused by the sudden collapse of an overly massive neutron star. The event is caused by a previous merger of two neutron stars; this creates an unstable intermediate neutron star, which does not immediately collapse due to its rapid rotation.
In a blitzar, the neutron star’s strong magnetic fields slow its rotation, causing it to collapse into a black hole several hours after the merger. The collapse suddenly turns off the dynamo that powers the magnetic fields, releasing their energy in the form of a fast radio burst.
So the events we have lumped together as FRBs may actually be the product of two different events. The repeating events take place in the environment around a magnetar. The one-off events are caused by the death of a highly magnetized neutron star within a few hours of its formation. Astronomers last year announced the detection of a possible blitzar possibly related to an FRB.
Only about 3 percent of FRBs are of the repeating variety. According to Pandhi, this is the first analysis of the remaining 97 percent of non-repeating FRBs, using data from Canada’s CHIME (Canadian Hydrogen Intensity Mapping Experiment) instrument. CHIME was built for other observations, but is sensitive to many of the wavelengths that make up an FRB. Unlike most radio telescopes, which focus on small points in the sky, CHIME scans a huge area, allowing it to spot FRBs even though they almost never appear in the same place twice.
Pandhi et al. decided to investigate how the light polarization direction of 128 non-repeating FRBs changes to learn more about the environments in which they emerged. The team found that the polarized light from non-repeating FRBs changes both with time and with different colors of light. They concluded that this particular sample of non-repeating FRBs is either a separate population or more evolved versions of these types of FRBs that are part of a population that originated in less extreme environments with lower burst rates. This is consistent with the idea that non-repeating FRBs are quite different from their rarer repeating FRBs.
The Astrophysical Journal, 2024. DOI: 10.3847/1538-4357/ad40aa (About DOIs).