A source of powerful radio signals from deep space has deepened the mystery of fast radio bursts. An analysis of data collected from the fast radio burst source FRB121102 in 2019 showed that 1,652 bursts were generated in just 47 days.
Setting a record for the greatest activity of a fast radio burst source, the observations provided enough detail to conduct a thorough search for periodicity – regular intervals of time between such bursts.
No evidence of periodicity was found, which the researchers say makes it very difficult to narrow down the source to a rotating compact object such as a highly magnetic dead star, or magnetar.
This suggests that there may be more than one mechanism causing these powerful bursts of radiation, and that we have a long way to go before we figure it all out.
Since their discovery in 2007, fast radio bursts have kept astronomers busy. As the name implies, they are bursts of light in the radio band that burst very quickly, in just a few milliseconds.
Most of them, which we can trace to the source, originate from galaxies millions and billions of light-years away, but they are incredibly powerful: in those milliseconds, a fast radio burst can release as much energy as hundreds of millions of suns.
Most often, sources of fast radio bursts erupt once and then we usually never hear from them again, so they are impossible to predict and very difficult to track. We don’t know what causes them, although a recent discovery right here in our home galaxy points to a type of neutron star called a magnetar.
But several sources of fast radio bursts have been rediscovered, and they may be one of the clues that can help at least partially solve this mystery.
The first and most numerous of them is FRB 121102. Its recurrence has allowed astronomers to track it to a dwarf galaxy 3 billion light-years away, and it’s a real oddball. Not only is it incredibly active, its activity is on a cycle – 90 days of activity, then 67 days of silence.
Such abundant activity means that we have been able to catch FRB 121102 in the act quite often, but the detections made with the five-hundred-meter aperture spherical radio telescope (FAST) have exceeded all expectations.
During the commissioning phase of the telescope, from Aug. 29 to Oct. 29, 2019, it recorded 1,652 separate bursts from the hyperactive object over a 59.5-hour period.
The peak frequency was 122 bursts in one hour, the highest level of activity we have ever observed in sources of fast radio bursts.
This huge number of detections allowed a statistical analysis of the source activity. The researchers found that the bursts could be divided into two different types: higher-energy and lower-energy bursts exhibited completely different properties, and weak bursts were more random in nature.
The data also allowed us to find periodicity in the bursts ranging from 1 millisecond to 1000 seconds. Given that magnetars have rotational speeds within this time frame, if the bursts were caused by a mechanism on the surface of the star, it should have appeared periodically – think of a rotating lighthouse.
However, nothing like that was found in the data. This means that magnetars may not be the only source of fast radio bursts.
Astronomers already suspect this, though; different sources show significant differences in the nature of the bursts, their strength, duration, repetition, and polarization (which means they may be emitted from completely different environments).
Thus, in addition to figuring out the exact mechanism underlying the magnetar bursts, scientists definitely have work to do to figure out everything else. We will continue to monitor this space – and FRB 121102.
The study was published in the journal Nature.