HomeScience and NatureAstronomers Capture Reverse Shock Emission from Record-Breaking Gamma-Ray Burst

Astronomers Capture Reverse Shock Emission from Record-Breaking Gamma-Ray Burst

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Astronomers have provided vital information in the global effort to understand GRB 221009A, one of the nearest and possibly the most-energetic gamma-ray burst ever observed.

ESA’s XMM-Newton X-ray observatory recorded 20 dust rings, 19 of which are shown here in arbitrary colors. The image merges observations made two and five days after GRB 221009A erupted. Dark stripes indicate gaps between the detectors. A detailed analysis shows that the widest ring visible here, comparable to the apparent size of a full Moon, came from dust clouds located about 1,300 light-years away. The innermost ring arose from dust at a distance of 61,000 light-years — on the other side of our Galaxy. Image credit: ESA / XMM-Newton / M. Rigoselli, INAF.

GRB 221009A, a gamma-ray burst detected on October 9, 2022, is one of the nearest and possibly the most-energetic gamma-ray burst ever observed.

Dubbed as BOAT (brightest of all time),it occurred approximately 2.4 billion light-years away in the direction of the constellation Sagitta and was likely triggered by a supernova explosion giving birth to a black hole.

“The exceptional brightness of this gamma-ray burst meant astronomers were able to study it in unprecedented detail in real-time as the light arrived from that distant galaxy,” said James Leung, a Ph.D. student at the University of Sydney.

“This gave us a golden opportunity to test intricate physical models that describe what happens before, during and after the death of a star.”

“While that’s a bit of an exaggeration, GRB 221009A was likely the brightest burst at X-ray and gamma-ray energies to occur since human civilization began,” said Dr. Eric Burns, an astronomer at Louisiana State University.

GRB 221009A was so bright it blinded most gamma-ray instruments in space, which meant they could not measure the real intensity of the emission.

And while the energy from this gamma ray burst was not unusually large, the jets of energy were exceptionally narrow with one pointed directly at Earth, making it appear exceptionally bright.

This illustration shows the ingredients of a long gamma-ray burst, the most common type; the core of a massive star (left) has collapsed, forming a black hole that sends a jet of particles moving through the collapsing star and out into space at nearly the speed of light; radiation across the spectrum arises from hot ionized gas (plasma) in the vicinity of the newborn black hole, collisions among shells of fast-moving gas within the jet (internal shock waves),and from the leading edge of the jet as it sweeps up and interacts with its surroundings (external shock). Image credit: NASA’s Goddard Space Flight Center.

In a new paper, the astronomers present radio follow-up observations of GRB 221009A with the Arcminute Microkelvin Imager Large Array (AMI-LA) and Allen Telescope Array (ATA).

“One of the fascinating things about gamma ray bursts is, although they are over quite quickly — in just a matter of seconds — they leave afterglow emissions across the light spectrum in surrounding matter that echo for months and years afterwards,” said Professor Tara Murphy, an astronomer at the University of Sydney.

“This afterglow is produced by a forward shock from the material ejected by the gamma-ray burst and a reverse shock reflected backwards into the ejected material,” Leung said.

“This gives us further opportunities to observe these fascinating, powerful events.”

The new observations showed a rapid, early brightening from the source of the event caused by the reverse shock of the gamma ray burst.

This revealed evidence in radio waves that is difficult to explain within current theoretical explanations of gamma ray bursts.

“Our observations provide unmatched insights into the reverse shock model for gamma-ray burst emission, showing it is very difficult for existing models to replicate the slow evolution of the energy peaks that we observed,” Leung said.

“This means we have to refine and develop new theoretical models to understand these most extreme explosions in the Universe.”

This detective work will help astronomers quickly pinpoint future gamma ray bursts, perhaps assisting in the discovery of predicted supernovae associated with the events.

“The most interesting part of a cosmic explosion is the very beginning as the explosion expels material that is moving at nearly the speed of light,” said Dr. Gemma Anderson, an astronomer at ICRAR and Curtin University.

“We therefore want the radio telescopes to be on target and observing GRBs as quickly as possible so that we can detect the very earliest radio light they emit.”

The paper will be published in the journal Nature Astronomy.


Joe S. Bright et al. 2023. Precise Measurements of Self-absorbed Rising Reverse Shock Emission from Gamma-ray Burst 221009A. Nature Astronomy, in press; arXiv: 2303.13583

Source : Breaking Science News

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