A source of powerful radio signals from deep space has deepened the mystery of rapid radio bursts.
An analysis of data collected on the rapid radio burst source FRB121102 in 2019 found 1,652 spitting eruptions in just 47 days.
Setting a record for the greatest activity exhibited by a rapid radio burst source to date, the observations provide enough detail to conduct a thorough search for periodicity – regular time intervals between similar bursts.
No sign of periodicity has been found, which the researchers say poses significant challenges in reducing the source to a rotating compact object, such as a highly magnetic dead star or magnetar.
This strongly suggests that there may be more than one mechanism producing 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, rapid radio bursts have baffled astronomers. As their name suggests, these are bursts of light in the radio spectrum that light up extremely quickly, lasting only a few milliseconds.
Of those that we can trace to a source, most have origins in galaxies millions to billions light years away, but they are incredibly powerful; in these milliseconds, a rapid radio burst can discharge as much power as hundreds of millions of suns.
Most of the time, the sources of fast radio bursts light up once, and then we tend to not hear about them again, making them impossible to predict and very difficult to trace. And we don’t know what causes them, although a recent detection right here in our home galaxy points quite strongly to a type of neutron star called magnetars.
But one a handful of sources of rapid radio bursts have been detected repeating themselves, and these could be one of the keys that help to at least partially solve the mystery.
Of these, the first and most prolific is FRB 121102. Its repetition has allowed astronomers to trace it to a dwarf galaxy 3 billion light-years away, and it’s a real nutcase. Not only is he incredibly active, his activity occurs on a cycle – 90 days of activity, then 67 days of silence.
This abundant activity means we were able to catch FRB 121102 in the act. a lot, but the detections made using the spherical radiotelescope with aperture of five hundred meters (QUICK) blew them all out of the water.
During the telescope’s commissioning phase, between August 29 and October 29, 2019, it captured 1,652 individual bursts from the hyperactive object, for a total of 59.5 hours.
The peak rate was 122 bursts over the course of an hour – the highest level of activity we’ve ever seen in a rapid radio burst source.
This massive collection of detections allowed a statistical analysis of the activity of the source. The researchers found that bursts could be classified into two different types, with higher energy and lower energy bursts showing markedly different properties, with weaker ones being more random in nature.
The data also allowed a search for periodicity in the bursts between 1 millisecond and 1000 seconds. Since magnetars have spinning rates in this period, if the bursts were caused by some mechanism on the star’s surface, they should have appeared periodically – think of a spinning lighthouse.
No such thing, however, was found in the data. This means that magnetars may not be the only source of rapid radio bursts.
Astronomers already suspect it, however; there is significant variation in the pattern, strength, duration, repetition, and polarization of the bursts (meaning they could be emitted by very different types of environments) between sources.
So in addition to figuring out the exact mechanism behind magnetar bursts, scientists certainly have their work cut out for them in figuring out the rest. We will continue to monitor this space – and FRB 121102.
The research was published in Nature.