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Record bright gamma-ray burst. The brightest since the beginning of human civilization

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A gamma-ray burst recorded last October may have been the brightest ever observed. GRB 221009A “blinded” even some measuring instruments, which made its study difficult. Researchers say such bright events may occur on average once every 10,000 years.

On Sunday, October 9, 2022, a flash of extremely intense radiation swept through the solar system. Its source was a gamma-ray burst, one of the strongest class of bursts in the Universe. Only now scientists have managed to get to all the data that helped determine how bright the flare was. The results of their work have been published in The Astrophysical Journal Letters.

A monstrously bright flash

To characterize the burst, which has been dubbed GRB 221009A, scientists used data from multiple measurement instruments – the Fermi GST space gamma-ray observatory, the International Space Station’s NICER telescope and even Voyager 1. This was necessary because the phenomenon was so bright that “blinded” most of the cosmic measuring instruments, so they only partially registered them. Researchers first had to reconstruct the missing data, and only then proceeded to analyze the phenomenon.

Before the signal from GRB 221009A reached Earth, it traveled for about 1.9 billion years, making it one of the closest “long” bursts with an initial emission of more than two seconds. It was 70 times brighter than any other observed so far. From a statistical point of view, such bright events can occur on average once every 10,000 years.

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“GRB 221009A is probably the brightest X-ray and gamma-ray outburst that has occurred since the dawn of human civilization,” said Eric Burns, of Louisiana State University and the study’s lead author. “It’s a truly monstrous explosion, incredibly unusual. We’ve never seen anything close to it.

Location of GRB 221009A. From the perspective of an observer on Earth, the flare came from the direction of the constellation ArrowNASA/ESA/CSA, STScI/A. Levan/G Kober

The first breath of a black hole

Astronomers believe that such flares represent the “first breath” of black holes. As the cores of massive stars collapse under their own weight, engulfing the surrounding material, the dying celestial body ejects jets – jets of particles near the speed of light – in opposite directions. They pierce the star, traveling through space and emitting X-rays and gamma rays.

Although GRB 221009A looked like the first harbinger of a supernova, so far scientists have been unable to find any traces of a cosmic explosion. Researchers have several hypotheses as to why this happened: one is that the flare occurred in a part of the sky close to our galaxy’s plane, where the light may have been obscured by dense clouds of dust.

“We can’t definitely say it’s a supernova, which is surprising given the brightness of the explosion,” said Andrew Levan of Radboud University, who supervised the James Webb Space Telescope’s observations of the blast site. – If it’s there, it’s very weak. We plan to keep looking for it, but it’s possible the star collapsed into a black hole instead of exploding.

Visualization of gamma-ray bursts and jetsNASA’s Goddard Space Flight Center

The stream was heading straight for us

The relatively close, bright flare also provided an opportunity to better observe the jets that are emitted during the flare and the accompanying phenomena. In the case of GRB 221009A, they were not particularly powerful, but they turned out to be extremely narrow, like a stream of water from a garden hose. One of them was aimed directly at us, which made it possible to collect a complete set of information about the electromagnetic spectrum of this phenomenon.

The flare allowed astronomers to study the clouds of cosmic dust in our galaxy. As the X-rays headed our way, some of them bounced off the dust, creating a “light echo” of the flare in the form of rings. The European Space Agency’s XMM-Newton telescope recorded that these unusual rings were produced by 21 separate dust clouds. Previously, such a phenomenon had been observed only six times.

‘How dust clouds scatter radiation depends on their distance, the size of the dust grains and the energy of the radiation,’ explained Sergio Campana of the National Institute of Astrophysics in Italy. “We were able to use the rings to reconstruct the X-ray part of the explosion emission and to determine where the dust clouds are in our galaxy,” he added.

The gamma-ray burst GRB 221009A has highlighted clouds of cosmic dustESA/XMM-Newton/M. Rigoselli (INAF)

Main photo source: ESA/XMM-Newton/M. Rigoselli (INAF)

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