Astronomers Accurately Predict Timing Of Gamma-Ray Bursts From A Magnetar

Artist impression of gamma-ray emission from a neutron star.  Image Credit: sakkmesterke/Shutterstock.com

Magnetar SGR1935+2154 is currently a unique object in our own Milky Way. It is the only known source of fast-radio bursts (FRBs) in our galaxy, as well as emitting gamma-ray bursts. Researchers estimated that its gamma-ray activity will be paused for a while before resuming in June – and the stellar object did as predicted. It began emitting gamma-rays right on schedule.

The prediction of the bursts was first published in a pre-print back in March. Based on data collected since 2014, the team expected SGR 1935+2154 to not emit a burst earlier than June 1. The burst came on June 24 – since then, 12 more were recorded, and the scientists predict the window of activity to continue until October 7. The paper was also published in Physical Review D.

“These new bursts within this window means that our prediction is dead on,” co-author Dr Bruce Grossan, from the University of California, Berkeley, said in a statement. “Probably more important is that no bursts were detected between the windows since we first published our preprint.”

The data comes from the WIND spacecraft, launched in 1994. Over the last 7 years, it detected all the brightest bursts from the magnetar. Periodic behavior has been witnessed from such objects, so the team considers that this might be the case for SGR1935+2154. However, the team was concerned that maybe the gap in the data was not due to that.

They say they approached in a similar way as the famous Sherlock Holmes quote about “the curious case of the dog in the nighttime” – not seeing the bursts could be just as important as seeing them. Hence, the idea that it has a periodic window of activity. Based on the analysis, the team estimates that the periodic behavior of SGR1935+2154 is the correct scenario with 99.97 percent certainty.

“Missing or occasional data is a nightmare for any scientist,” explained lead author Mikhail Denissenya, from Nazarbayev University. “In our case, it was crucial to realize that missing bursts or no bursts at all carry information.”

SGR1935+2154 is a neutron star with an impressive magnetic field. Such stellar objects are the product of supernovae. Fast-radio bursts are incredible emissions of radio waves that last for just a millisecond. It would take our Sun about 10,000 times longer to produce an equivalent energetic output. Some repeating FRBs are believed to be caused by magnetars orbiting another object, occasionally sending those emissions toward Earth.

“Magnetars, which are connected with fast radio bursts and soft gamma repeaters, have something periodic going on, on top of randomness,” added Grossan. “This is another mystery on top of the mystery of how the bursts are produced.”

This object is located 30,000 light-years away and it was behind FRB 200428. Given its relatively close location (all the others are extragalactic) it could well be revolutionary in our understanding of FRBs.

 


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