Scientists Record GRB 221009A, the Brightest Gamma-Ray Burst in Cosmic History
A team of scientists from 17 countries, including physicists from HSE University, analysed early photometric and spectroscopic data of GRB 221009A, the brightest gamma-ray burst ever recorded. The data was obtained at the Sayan Observatory one hour and 15 minutes after the emission was registered. The researchers detected photons with an energy of 18 teraelectronvolts (TeV). Theoretically, such high-energy particles should not reach Earth, but data analysis has confirmed that they can. The results challenge the theory of gamma radiation absorption and may point to unknown physical processes. The study has been published in Astronomy & Astrophysics.
Gamma-ray bursts are the most powerful cosmic explosions, releasing an immense amount of energy. These bursts were first detected in the gamma range, giving them their name. They occur during the death of massive stars or the collision of neutron stars.
On October 9, 2022, several space-based gamma-ray observatories detected an exceptionally bright burst, later classified as GRB 221009A—the most powerful gamma-ray burst ever recorded. The burst's unprecedented brightness was so intense that it caused malfunctions in the gamma-ray telescopes of most orbital observatories, including Fermi, INTEGRAL, and Konus-Wind. In addition, the gamma radiation that reached Earth caused a significant disturbance in the ionosphere.
The radiation energy emitted by GRB 221009A over just one hundred seconds was equivalent to the combined radiation of one billion Suns over 97 billion years, even though the age of the Universe is only 13.8 billion years. Such events occur extremely rarely—once in a thousand years. However, it wasn't just the brightness that made GRB 221009A unique. The burst occurred 2.4 billion light-years from Earth, which is relatively close by the standards of the Universe. For comparison, the most distant known burst was recorded at a distance of approximately 13.2 billion light-years. As a result, the event sparked significant interest in the scientific community: by the end of 2022, seven papers had been published, and now there are more than 200.
Researchers are continuing to analyse data on GRB 221009A. For the first time, an international team of scientists from 17 countries, including researchers from HSE University, analysed data from photometric and spectroscopic observations collected at the Sayan Observatory one hour and 15 minutes after the gamma-ray burst was detected.
Photometric and spectroscopic observations are methods used to measure the intensity of electromagnetic radiation in the visible and infrared ranges, as well as its 'colour composition' (spectrum). The former makes it possible to determine the brightness of an object, while the latter reveals the chemical elements present in the emitting object and along the radiation path to the observer.
According to the scientists, the data analysis suggests prolonged activity of the central engine—a compact, massive object responsible for generating gamma-ray burst radiation. They also note that the environment surrounding the explosion changed from a denser one, shaped by the stellar wind, to a more rarefied one, similar to the interstellar medium.
The researchers were particularly interested in photons with an energy of 18 teraelectronvolts (TeV), which were recorded from the GRB 221009A source by the Large High Altitude Air Shower Observatory (LHAASO). Theoretically, such high-energy photons should not be detectable due to their interaction with optical photons in the intergalactic medium on their way to the observer; however, they somehow still reached Earth. The analysis reveals that the detection of photons with an energy of 18 TeV is unlikely according to existing models of intergalactic background radiation, and their detection from gamma-ray burst sources remains a unique occurrence.
Sergey Belkin
'The detection of high-energy photons allows us to test fundamental laws of physics, such as the constancy of the speed of light. However, there is no cause for concern yet, as the detection of such high-energy photons can still be explained by uncertainties in the intergalactic background radiation model, rather than a violation of Lorentz invariance—the fundamental principle stating that the speed of light is constant in all reference frames,' explains Sergey Belkin, doctoral student at the Joint Department of Space Physics with the Space Research Institute (RAS) of the HSE Faculty of Physics.
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