Fast Radio Bursts (FRB) are mysterious powerful emissions of radio waves. In just a few milliseconds, the energy it takes the Sun to produce in a day is released, traveling across galaxies. Most of these events detected are one-offs but a few are known to repeat, though there is no discernable pattern so they are unpredictable and difficult to study. Scientists are now realizing that their repetition may not be random at all.
Observations from the CHIME collaboration now published in Nature have shown that the pattern of emission from FRB 180916 repeats every 16.35 days, with the whole burst arriving in less than a 5-day window followed by radio silence for the following days. They also discovered that 50 percent of the bursts are actually emitted over less than 15 hours within that first window. This is the first FRB detected that has regular repeating radio bursts, and both offers insights and furthers the mystery of these events.
Since its discovery on September 16, 2018, to last February, a team has been using the CHIME (Canadian Hydrogen Intensity Mapping Experiment) telescope to observe FRB 18091 to try and understand what kind of phenomenon might be behind the curious observations.
"This FRB we're reporting now is like clockwork," collaboration member Kiyoshi Masui, assistant professor of physics at MIT's Kavli Institute for Astrophysics and Space Research, said in a statement. "It's the most definitive pattern we've seen from one of these sources. And it's a big clue that we can use to start hunting down the physics of what's causing these bright flashes, which nobody really understands."
The source of the FRB is believed to be a compact object, such as a neutron star and it is located on the edge of a spiral galaxy 500 million light-years away. The team announced the discovery of the unusual periodicity earlier this year and now the newly published paper expands on the observations and adds more insight into this system. The data paints an interesting picture for the source of this FRB; it was not something previously expected.
The team suggests two main scenarios to explain the repeating cycle observed. Either the system is angled in a way that we only see the burst for a fraction of the time it's emitted (ie for the 4-5 days out of 16 days) or it might be affected by an orbiting companion. The first explanation has several issues, but the team says that there are many uncertainties surrounding the discovery and so it cannot be completely discounted.
The latter scenario instead plays out in a different way. If there is a companion, it might be releasing material stopping the radio emission when the source is too close, so the signal only gets through when it is far away. Or it might be the opposite case, that the FRBs are emitted closer to the companion possibly due to interactions. The possibility for companions is also varied if it's a regular star, a neutron star, or a black hole.
Possible periodic activity was recently reported for another repeating FRB, FRB 121102. However, its period is almost 10 times longer and the orbiting companion explanation is favored for that event.