Pressroom – Analysis of an extraordinary cosmic explosion

“Gamma-ray bursts are flashes of X-ray and gamma-ray light observed in the sky, emitted from sources far beyond the galaxy.“Says Edna Ruiz Velasco of MPIK in Heidelberg, Germany, one of the corresponding article authors.”These are the most violent explosions in the universe, and explosions lasting more than a few seconds are likely related to the collapse of a massive star into a black hole.“.

Burst emissions are divided into two distinct phasess : An initial, chaotic phase lasting a few tens of seconds, followed by a later long-lasting phase that slowly fades away.

The exceptional observation of a gamma-ray burst was among the closest ever recorded

On August 29, 2019, the Fermi and Swift satellites detected a gamma-ray burst in the constellation Eridanus. The event, classified as GRB 190829A, according to its start date, turned out to be lOne of the closest gamma-ray bursts seen so far, about a billion light-years away. For comparison, typical eruptions are about 20 billion light-years away. The team captured the afterglow of the eruption as soon as it became visible to the HESS (High Energy Stereoscopic System) telescopes in Namibia.

The signal was strong enough to be detected instantly! This allowed us to quickly inform the international community,” Fabian Schusler, CEA-Irfu, coordinator of the team responsible for gamma-ray burst analysis.

The relatively small distance of the gamma-ray burst made it possible to measure in detail the spectrum of the afterglow, that is, the distribution of the energies of the radiation photons. The spectrum of GRB 190829A was thus determined to have an energy of 3.3 TeV, or nearly a trillion times the energy of visible light photons. This is the highest energy recorded from a gamma ray burst so far.

Because GRB 190829A occurs in the cosmic backyard, the very high energy photons are not absorbed by collisions with background light on their way to Earth, as they do at greater distances.

An observation that raises questions about the theory of gamma ray bursts in the universe

HESS was able to follow the aurora for up to three days after the initial eruption. ‘, Fabian Schusler

The result was surprising: Observations revealed curious similarities between the extremely high energy of X-ray emissions and gamma rays from the afterglow of the explosion.. Contrary to well-established theories assuming that the two emission elements must be produced by separate mechanisms, observations of the afterglow of GRB 190829A show that the X-rays and gamma rays simultaneously decreased.

Furthermore it, It is clear that the gamma ray energy spectrum corresponds to the extrapolation of the X-ray spectrum. These results indicate that the high-energy X-rays and gamma rays of this afterglow were produced by the same mechanism and at the same time.

© DESY – Science Communication Lab

“The scope of this possibility highlights the need for further studies on the subsequent emission of high-energy gamma-ray bursts.”, notes Mathieu de Noroy, deputy director of the HESS Observatory and researcher at LLR, France.

GRB 190829A is the fourth gamma ray burst detected from Earth. However, the previously detected eruptions occurred much further into the universe and their subsequent auroras can only be observed for a few hours each and not at energies greater than 1 TeV.

© DESY – Science Communication Lab

Theprospects for detectionIon bursts of gamma rays by next-generation devices appear promising : Scientists expect regular discoveries in the very high energy range to become common with improved instruments, which will help to fully understand these massive cosmic explosions.