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DIAS scientists help reveal ‘exceptional’ cosmic blast in unprecedented detail

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

An international team of scientists, including researchers from the Dublin Institute for Advanced Studies (DIAS), have gained the best view ever recorded of gamma-ray bursts – the brightest explosions in the universe. The findings were published in Science today (03.06.21).

DIAS is a co-founder of the High Energy Stereoscopic System (H.E.S.S) – a specialised observatory located in Namibia – which was able to record the event due to its enhanced Cherenkov telescopes. The team of researchers involved in the discovery, includes Prof. Felix Aharonian, Professor in Astronomy and Astrophysics at DIAS and Dr. Jonathan Mackey, a DIAS research fellow. Dr Andrew Taylor a former Schrodinger fellow at DIAS, and Dr. Carlo Romoli, a former PhD student at DIAS are also corresponding authors of the paper. 

The event, catalogued as GRB 190829A according to its date of occurrence 29th 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.

Challenging gamma-ray burst theories

Fading afterglow emission at TeV energies during the period of observation (from H.E.S.S. paper)

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.

Commenting today (03.06.21) Prof. Felix Aharonian, said: “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. 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. Jonathan Mackey, a DIAS research fellow, also working on the H.E.S.S project, 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.”

DIAS connection

Commenting on the role of DIAS in the H.E.S.S project, Dr. Eucharia Meehan CEO and Register of DIAS, said: “I would like to congratulate the DIAS researchers for their important role in this discovery which has enhanced our knowledge of the universe we inhabit. This successful international research collaboration again highlights how highly regarded DIAS is on an international stage. I look forward to DIAS participating in future research projects to strengthen our understanding of gamma-ray bursts.”

More than 230 scientists from 41 institutes in 15 countries (Namibia, South Africa, Germany, France, the UK, Ireland, Italy, Austria, the Netherlands, Poland, Sweden, Armenia, Japan, China and Australia) contributed to this research.

To read more about the findings of the H.E.S.S please read the full article in Science here.

About H.E.S.S.

H.E.S.S. is a system of five Imaging Atmospheric Cherenkov Telescopes that investigates cosmic gamma rays. The name H.E.S.S. stands for High Energy Stereoscopic System, and is also intended to pay homage to Victor Franz Hess, who received the Nobel Prize in Physics in 1936 for his discovery of cosmic radiation. H.E.S.S. is located in Namibia, near the Gamsberg mountain, an area well known for its excellent optical quality. Four H.E.S.S. telescopes went into operation in 2002/2003, the much larger fifth telescope – H.E.S.S. II – is operational since July 2012, extending the energy coverage towards lower energies and further improving sensitivity. In 2015-2016, the cameras of the first four H.E.S.S. telescopes were fully refurbished using state of the art electronics and in particular the NECTAr readout chip designed for the next big experiment in the field, the Cherenkov Telescope Array (CTA).