Repetitive fast radio flash appears to be heard regularly

After 90 days of activity, the source takes 67 days of rest. And then start all over again.

Researchers come to this conclusion after examining as many as 32 bursts of the fast radio flash FRB 121102. Their findings can be read in the magazine. Monthly Notices of the Royal Astronomical Society.

Surprisingly
The previously extensively studied radio flash FRB 121102 was already known to have erupted repeatedly, but researchers did not immediately see that there were regularities in those bursts. “We were certainly surprised,” said researcher Kaustubh Rajwade, talking to Scientias.nl. “FRB 121102 has been observed by radio telescopes around the world for a while now and several attempts have been made to find regularity in its successive pulses and until recently it was unsuccessful. Nobody expected that there would be regularity in the activity of this source. ”

However, FRB 121102 does have regularity. That was apparent when Rajwade and colleagues made observations of the Lovell Telescope in Britain combined with observations from other telescopes. They found that FRB 121102 is active in a 90-day period each time, with no activity for 67 days thereafter. That 157-day cycle then repeats continuously.

FRB 180916.J10158 + 56
FRB 121102 is only the second repetitive fast radio flash that is heard very regularly. The first – FRB 180916.J10158 + 56 – was recently discovered using a telescope in Canada. However, the cycle of this fast radio flash lasts only sixteen days. That means FRB 121102 has an almost ten times longer cycle! It is still unclear how this difference can be explained.

Origin
Rajwade and colleagues hope that studies of regularity in the activity of repetitive high-speed radio flashes can provide more insight into how these energetic bursts in space occur (see box).

About fast radio flashes
Rapid radio flashes are massive bursts in space, releasing more energy – roughly 1 millisecond – in a short time than our sun has generated in 80 years. Researchers do not know exactly how fast radio flashes occur. The first fast radio flash was detected in 2007 and quite a few fast radio flashes have been observed in the meantime. Some of these – such as FRB 121102 – make themselves heard repeatedly. Others seem to do that only once. It is also unknown whether the repetitive and non-repetitive fast radio flashes occur in the same way or in reality are two completely different phenomena.

At present there are several theories that could explain the occurrence of repetitive fast radio flashes – such as FRB 121102. The discovery that the bursts of some high-speed radio flashes follow a real cycle, and that the cycle can last quite a long time, can now be used to re-examine these theories and perhaps even exclude some of them. Rajwade then thinks, for example, of the theory that the wobbling movement of the axis of rotation of neutron stars relative to their vertical axis underlies rapid radio flashes. “This move can explain a period of several weeks.” But the cycle of FRB 121102 lasts not just a few weeks, but 157 days. “If we assume that FRBs are created by neutron stars, it is difficult to explain the 157-day period purely through the precession of a neutron star.” While it is too early to serve the wobbling neutron star as a source of FRBs, Rajwade thinks other theories are more in line with what FRB 121102 shows. “What we suggest is that the periodicity is caused by the movement of the object causing these FRBs around another astrophysical object – for example, a massive star, a neutron star or even a black hole. So it is the job movement that causes this periodicity. ”

More research
However, more research is urgently needed to pinpoint the source of these FRBs. “The detection of periodicity in two FRBs raises the question of whether all repeating FRBs exhibit this behavior,” Rajwade said. “We need to track down and monitor more repetitive high-speed radio flashes to find out what they have in common and to better understand the trends in the frequency of repetitive high-speed radio flashes. This in turn helps us to get a better grip on their origin. ”

Fast radio flashes that apparently only sound once, also deserve our attention. Some researchers suspect that all fast radio flashes in reality repeatedly make an appearance, but the one-off copies do that less often or not always as powerful. The discovery that the cycles of proven repetitive high-speed radio flashes can indeed vary widely may seem to cautiously endorse that idea. But Rajwade doesn’t want to go that far. “Whether all FRBs rehearse is still the question. It is certainly possible, but we cannot say it with certainty at this time. Only more and more discoveries will lead to an answer to that question. ”

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