Soft Gamma Rays Flicker Chaotically in Time Windows

by | Jul 21, 2021 | Daily Space, Fast Radio Bursts, Neutron Stars / Pulsars | 0 comments

IMAGE: Since 2014, a magnetar in our galaxy (SGR1935+2154) has been emitting bursts of soft gamma rays (black stars). UC Berkeley scientists concluded that they occurred only within certain windows of time (green stripes) but were somehow blocked during intervening windows (red). They used this pattern to predict renewed bursts starting after June 1, 2021 (stripes outlined in blue at right), and since June 24, more than a dozen have been detected (blue stars): right on schedule. CREDIT: Mikhail Denissenya, Nazarbayev University, Kazakhstan

Astronomy is a long game, and sometimes, keeping our eyes on things across decades allows weird new phenomena to be discovered. The star SGR1935+2154 is a neutron star that periodically gives off gamma-ray radiation. It is thought this star has a powerful magnetic field, and that magnetic field periodically does something we can’t describe, and that something gives off gamma rays. Most of the time, these events are just enough to get the star noticed, but periodically, the events are briefly very powerful in radio light. This makes SG1935+2154 the only known fast radio burst source in our Milky Way galaxy.

Regularly observed since 2014, it was initially noticed that this object can flicker with bursts of soft gamma rays, sometimes one right after another and sometimes with long quiet periods. While random flickering can have a pattern, it was noticed over the years that this object would flicker away for about four months and then go silent for three months. This is like turning chaotically blinking Christmas lights off and on over the seasons.

This kind of windowing behavior is not something we’re used to seeing in astronomy. It’s not like stars hibernate or anything. The question has to be asked: is this real or just random chance?

On March 19, the team put out a pre-print that predicted that SGR1935+2154 would be quiet until June when it would start flickering again, and on June 24 the first of what have been many flickers have been observed. According to researcher Bruce Gossan: These new bursts within this window means that our prediction is dead-on. Probably more important is that no bursts were detected between the windows since we first published our preprint.”

Since 2014, they have observed ten windowed periods of activity. Statistically, there is only a three in 10,000 chance that this occurred randomly.

Why are these occurring? We don’t know, and that is awesome; we have one more amazing mystery to track down. According to the release on this story: Grossan and Linder can only guess. Soft gamma-ray bursts from magnetars are thought to involve starquakes, perhaps triggered by interactions between the neutron star’s crust and its intense magnetic field. Magnetars rotate once every few seconds, and if the rotation is accompanied by a precession — a wobble in the rotation — that might make the source of burst emission point to Earth only within a certain window. Another possibility, Grossan said, is that a dense, rotating cloud of obscuring material surrounds the magnetar but has a hole that only periodically allows bursts to come out and reach Earth.

More Information

Galactic gamma ray bursts predicted last year show up right on schedule (EurekAlert)

Distinguishing time clustering of astrophysical bursts,” Mikhail Denissenya, Bruce Grossan, and Eric V. Linder, 2021 July 6, Physical Review D

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