A team of scientists has achieved the best view yet of the brightest explosions in the universe : gamma ray bursts (GRBs), associated with extremely energetic explosions in distant galaxies.
It has been a specialized observatory in Namibia that has recorded the most energetic radiation and the longest gamma ray glow from a gamma ray burst (GRB) to date. The cosmic explosion has been so colossal that observations with the High Energy Stereoscopic System (HESS) challenge the established idea of how gamma rays are produced in these colossal stellar explosions.
One of the most energetic phenomena in the universe
“Gamma-ray bursts are bright X-rays and gamma-ray flashes observed in the sky, emitted by distant extragalactic sources,” explains DESY scientist Sylvia Zhu, co-author of the work. “They are the largest explosions in the universe and are associated with the collapse of a massive, rapidly spinning star into a black hole. A fraction of the released gravitational energy fuels the production of an ultrarelativistic shock wave. Its emission is divided into two distinct phases: a chaotic and rapid initial phase that lasts tens of seconds, followed by a long-lasting glow phase that fades smoothly. “
The explosive event marked the death of a star and the beginning of its transformation into a black hole, according to experts from the German Electron Synchrotron in Hamburg. It was detected by the Fermi and Swift space telescopes, with the support of the High Energy Stereoscopic System (HESS) telescope in Namibia.
The explosion, named GRB 190829A, was first detected on August 29, 2019. Although this explosion is about 1 billion light-years away, it is believed to be in our cosmic region.
“The energy of the gamma rays was detected during several days” , explain the experts. Prior to this, gamma-ray bursts were generally detected around 20 billion light-years away (this time only 1 billion light-years away) and their glow could only be observed for a few hours each and at very high energies. lower.
“We were really sitting in the front row when this gamma-ray burst happened,” celebrates DESY co-author Andrew Taylor. The team caught the post-explosion glow immediately when it became visible to the HESS telescopes. “We were able to observe the afterglow for several days at unprecedented gamma ray energies,” says Taylor.
Its relatively short distance allowed detailed measurements of the glow spectrum , the distribution of ‘colors’ or energies of the radiation photons, in the very high energy range.
“We could determine the spectrum of GRB 190829A up to an energy of 3.3 tera-electron volts , which is approximately one trillion times more energetic than photons in visible light,” explains Edna Ruiz-Velasco of the Max Planck Institute for Nuclear Physics in Heidelberg.
The results
“Our observations revealed curious similarities between X-rays and the very high-energy gamma ray emission from the blast glow,” the authors comment.
The theory states that the two emission components must be produced by separate mechanisms. But afterglow observations from GRB 190829A show that both components, X-rays and gamma rays, faded in sync. This poses a challenge to the synchrotron origin of the very high energy gamma ray emission.
Referencia: Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow. Science 04 Jun 2021: Vol. 372, Issue 6546, pp. 1081-1085 DOI: 10.1126/science.abe8560
