Gamma-Ray Observatory Collects Best View of Cosmic Explosion

The imaging process by scientists captured the longest afterglow of a gamma-ray burst ever and only the fourth burst recorded from Earth.

Artist’s impression of a relativistic jet of a gamma-ray burst (GRB), breaking out of a collapsing star, and emitting very-high-energy photons. (Credit: DESY, Science Communication Lab)

(CN) — With help from powerful telescopes, a team of scientists gained an unprecedented front-row view of a gamma-ray burst shooting out from a collapsing star. The view of the high-energy explosion, among the largest in the universe, challenges our understanding of how gamma-rays are produced, according to a study released Thursday.

Study author Sylvia Zhu, a scientist at the Deutsches Elektronen-Synchrotron, a German research center that operates a particle accelerator, described gamma-rays and their origins in a statement released with the study published in the journal Science.

“Gamma-ray bursts are bright X-ray and gamma-ray flashes observed in the sky, emitted by distant extragalactic sources,” Zhu said. “They are the biggest explosions in the universe and are associated with the collapse of a rapidly rotating massive star to a black hole. A fraction of the liberated gravitational energy feeds the production of an ultrarelativistic blast wave. Their emission is divided into two distinct phases: an initial chaotic prompt phase lasting tens of seconds, followed by a long-lasting, smoothly fading afterglow phase.”

In 2019, the satellites Fermi and Swift detected a gamma-ray burst in the constellation of Eridanus.

The spectacular explosion was one of the nearest to Earth ever recorded, with a distance of about one billion light years. Typically, gamma-ray bursts have been recorded at about 20 billion light years from our planet.

“We were really sitting in the front row when this gamma-ray burst happened,” study coauthor Andrew Taylor of DESY said in the statement.

To capture the gamma-ray burst event — catalogued by scientists as GRB 190829A — the team of researchers directed the collective imaging power of the High Energy Stereoscopic System (H.E.S.S.) to the stars.

The system of telescopes located near Namibia’s Gamsberg Mountain managed to capture stunning detail of the gamma-ray burst, including its afterglow and the photon energy of its radiation, according to study co-author Edna Ruiz-Velasco from the Max Planck Institute for Nuclear Physics in Heidelberg, Germany.

“We could determine GRB 190829A’s spectrum up to an energy of 3.3 tera-electronvolts, that’s about a trillion times as energetic as the photons of visible light,” Ruiz-Velasco said. “This is what’s so exceptional about this gamma-ray burst — it happened in our cosmic backyard where the very-high-energy photons were not absorbed in collisions with background light on their way to Earth, as it happens over larger distances in the cosmos.”

The team was able to observe and capture details of the afterglow and its radiation signatures for several days. 

The three previous gamma-ray bursts recorded from Earth were much farther away in the cosmos and could only be observed for several hours, the scientists said, adding the energy signatures of those bursts never reached above 1 tera-electronvolts.

The H.E.S.S. observatory recording marked the most energetic radiation and longest afterglow captured from a gamma-ray burst in history. Researchers were struck by the very-high-energy gamma rays produced by the burst, which challenges traditional theories about the explosions and their ability to accelerate electrons enough to produce X-rays in a synchrotron process.

The process is similar to how particle accelerators such as the one managed by DESY produce bright X-rays for scientific investigations.

Scientists wrestled with their findings, which showed the X-ray and very-high energy gamma-ray emission of the burst’s afterglow are produced by the same mechanism within the burst.

“It is rather unexpected to observe such remarkably similar spectral and temporal characteristics in the X-ray and very-high energy gamma-ray energy bands, if the emission in these two energy ranges had different origins,” study co-author Dmitry Khangulyan from Rikkyo University in Tokyo said in the statement.

The scientists said more research is needed to understand afterglow emissions.

“Looking to the future, the prospects for the detection of gamma-ray bursts by next-generation instruments like the Cherenkov Telescope Array that is currently being built in the Chilean Andes and on the Canary Island of La Palma look promising,” H.E.S.S. spokesperson Stefan Wagner said. “The general abundance of gamma-ray bursts leads us to expect that regular detections in the very-high energy band will become rather common, helping us to fully understand their physics.”

Researchers did not immediately respond to a request for further comment on the study.

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