DIAS scientists display ‘exceptional’ images of cosmic blast

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New observation challenges established theory of gamma-ray bursts in the universe

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4 June 2021 | 0

Researchers from the Dublin Institute for Advanced Studies (DIAS) were part of an international effort to gained the best recorded view of gamma-ray bursts – the brightest explosions in the universe. 

The event, catalogued as GRB 190829A according to its date of occurrence 29 August 2019, is one of the gamma-ray bursts closest to Earth ever observed, at a distance of roughly one billion lightyears away. A typical gamma-ray burst is 40 billion lightyears away.

DIAS is a co-founder of the High Energy Stereoscopic System (HESS), a specialised observatory located in Namibia, which was able to record the event due to its enhanced Cherenkov telescopes.

 

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The comparatively short distance to this gamma-ray burst allowed detailed measurements of the afterglow’s spectrum, which is the distribution of colours or photon energies of the radiation, in the very-high energy range.

GRB 190829A’s spectrum could be determined up to an energy of 3.3 tera-electronvolts, which is about a trillion times as energetic as the photons of visible light. This marks the highest energy spectrum of a gamma-ray burst recorded to date.

The findings have also challenged the established idea of how gamma-rays are produced in these colossal stellar explosions.

The team involved in observing the event includes Prof Felix Aharonian, professor in astronomy and astrophysics at DIAS, Dr Jonathan Mackey, a DIAS research fellow.

“Since GRB 190829A happened in our cosmic backyard, it’s 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 universe,” said Prof Aharonian. “This enabled us to examine the explosion with an unprecedented level of detail – our findings challenge the conventional gamma-ray burst theory.

“According to existing theories it seemed very unlikely that even the most powerful explosions in the universe could accelerate electrons enough to directly produce the observed very-high-energy gamma rays. However, we were able to determine that the characteristics of the gamma-ray and X-ray radiation are strikingly similar, so that the simplest explanation is that they were produced together by the same radiation process.  This is quite unexpected and poses challenges to the prevailing theories of gamma-ray bursts.”

Dr Mackey added: “The far-reaching implication of this discovery highlights the need for further studies in this area. GRB 190829A is only the fourth gamma-ray burst detected from the ground at very high energies. Looking to the future, the prospects for the detection of gamma-ray bursts by next-generation instruments look promising, which will help us to fully understand these gargantuan cosmic explosions.”

More than 230 scientists from 41 institutes in 15 countries contributed to the research.

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