CHIME/Dunlap Institute
Astronomers have puzzled over the origin of mysterious fast radio bursts (FRBs) since they were first spotted in 2007. Now, for the first time, researchers will examine non-recurring FRBs, i.e. those that have produced only one burst of light so far. . The authors of a new paper published in The Astrophysical Journal looked specifically at the properties of the polarized light emitted from these FRBs, providing further insight into the origin of the phenomenon. The analysis supports the hypothesis that there are different origins for recurring and non-recurring FRBs.
“This is a new way to analyze the data we have about FRBs. “Instead of just looking at how bright something is, we’re also looking at the angle of the light’s vibrating electromagnetic waves,” said co-author Ayush Pandhi, a graduate student at the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics. “It gives you more information about how and where this light is produced and what it went through on its way to us over many millions of light years.”
As we mentioned earlier, FRBs involve a sudden burst of radio frequency radiation lasting only a few microseconds. Astronomers have over a thousand to date; some come from sources that repeatedly emit FRBs, while others seem to burst once and die down. You can create this kind of sudden energy surge by destroying something. But the existence of recurring sources suggests that at least some of them are produced by an object that survives the event. This 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 found that do not seem to repeat at all, suggesting that the conditions that create them may destroy their source. This is consistent with a blitzar – a bizarre astronomical event caused by the sudden collapse of an overly massive neutron star. The event is driven by the earlier merger of two neutron stars; this creates an unstable intermediate neutron star that is protected from immediate collapse by its rapid rotation.
In a blitz, the neutron star’s strong magnetic fields slow its rotation, causing it to collapse into a black hole hours after the merger. This collapse suddenly wipes out the dynamo’s powering magnetic fields and releases their energy in the form of a fast radio burst.
So the events we’ve been lumping together as FRBs could actually be the product of two different events. Recurring events occur in the environment around the magnetar. One-off events are triggered by the death of a highly magnetized neutron star within hours of its formation. Last year, astronomers announced the detection of a possible blitz potentially associated with FRBs.
Only about 3 percent of FRBs are of the repeating variety. Per Pandhi, this is the first analysis of the other 97 percent of non-recurring FRBs using data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME). CHIME was built for other observations, but is sensitive to the many wavelengths that make up FRBs. Unlike most radio telescopes, which focus on small points in the sky, CHIME scans a huge area, allowing it to pick out FRBs even though they almost never occur in the same place twice.
Pandhi et al. decided to investigate how the direction of polarization of light from 128 non-repeating FRBs changes to learn more about the environments in which they were produced. 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-recurring FRBs is either a separate population or more evolved versions of these kinds of FRBs that are part of a population that originated in less extreme environments with a lower burst frequency. This is consistent with the notion that non-recurring FRBs are quite different from their rarer recurring FRB counterparts.
The Astrophysical Journal, 2024. DOI: 10.3847/1538-4357/ad40aa (About DOI).