Elusive signal deepens the mystery of fast radio bursts

Astrophysicists have been baffled by fast radio bursts (FRBs), millisecond-long flurries of radio signals thought to come from deep in the cosmos.

A new study published in The Astrophysical Journal Letters has revealed major details about FRBs, specifically how they might be related to bursts of y-rays. The study team said their work could help to explain the origins of FRBs.

“If FRBs have γ-ray counterparts, it would be hugely constraining of models and extremely interesting,” Victoria Kaspi, an astrophysicist at McGill University who was not involved in the study, told Nature News.

Connecting the Bursts with Y-Rays

According to the report, researchers noticed that y-rays appeared almost simultaneously and from the same direction as a fast radio burst event called FRB 131104, named for the date it was seen: November 4, 2013.

Despite apparently being linked, the two signals tell different stories about their source, thought to be 10 billion light years away. While the FRB lasted a few milliseconds, the y-ray burst lasted between 2 and 6 minutes. The y-ray burst also contained much more energy than the FRB.

This has major ramifications for theories surrounding the source of FRBs. One primary theory has said FRBs are flares from remote magnetars, neutron stars with massive magnetic fields capable of producing brief, energetic blasts of energy, and do so consistently, as a minimum of one FRB is known to do. Despite the fact that magnetars are believed to generate y-rays, they would not give off such high energy and over that long a period of time.

“This is a severe challenge for magnetar models,” said study author Derek Fox, an astrophysicist at Penn State.

The y-ray signal did look like phenomena later recognized as coming from either a supernova or a supermassive black hole as it ingested a star, Fox said. The issue with both of these possibilities is that neither is known to create radio bursts.

A different possibility is that both signals came from a neutron star collision. However, that would not explain all FRBs, as neutron star collisions are considered to be fairly uncommon, while data suggests FRBs are quite frequent, happening around once every ten seconds.

It also isn’t clear the two detected signals came from the same source. Statistically, the possibility that the two signals would occur at the same time is just 1 in 800.The possibility of combined events does pass the statistical threshold required to conclude they are generated by the same source, but the finding is so unheard of – more evidence is needed, according to Kaspi.

“Extraordinary claims demand extraordinary evidence,” she said.

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Image credit: Spectrum Astro/NASA

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