The MAGIC telescopes detect the first burst of gamma rays In very high energies. This unprecedented observation provides new clues to understand the physical processes that occur in the most violent explosions in the universe. The results are published in two articles in the magazine Nature.
Gamma ray bursts (GRB) are the explodes more violent in the universe and they appear suddenly in the sky, approximately, once a day. They are believed to be the result of the collapse of massive stars or the fusion of neutron stars in distant galaxies. They begin with a very bright initial flash, called rapid emission, with a duration that varies from a fraction of a second to hundreds of seconds. This immediate emission is accompanied by a post-luminescence, a weaker, but longer lasting, emission over a wide range of wavelengths.
The first GRB detected by MAGIC telescopes, known as GRB 190114C, reveals the highest energy photons detected so far from these objects. This unprecedented observation provides the first evidence of a different emission process in the post-luminescence and provides new clues to understand the physical processes that occur in GRBs, which are still a mystery.
On January 14, 2019, two space satellites, the Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope, independently discovered a GRB. The outbreak was called GRB 190114C, and in 22 seconds, its coordinates in the sky were distributed in electronic alert form to astronomers around the world, including the MAGIC Collaboration, which operates two Cherenkov telescopes 17 meters in diameter located in the Roque de los Muchachos Observatory (Garafía, La Palma).
Since GRBs appear in unpredictable places in the sky and then quickly fade, your observation with telescopes such as MAGIC requires a dedicated tracking strategy. An automatic system processes real-time GRB alerts sent by satellites and makes MAGIC telescopes quickly point to the sky position where the GRB has been produced. María Victoria Fonseca, president of the MAGIC Collaboration Board highlights: "The telescopes were designed to be very light and move quickly. Despite weighing 64 tons each, they can rotate 180 degrees in just 25 seconds. Thanks to this, MAGIC began observing GRB 190114C only 50 seconds after its beginning. "
The analysis of the data collected during the first tens of seconds reveals the emission of photons in the post-luminescence that reach teraelectronvolt (TeV) energies, a billion times more energetic than visible light. During this time, the emission of TeV photons from the GRB 190114C was 100 times more intense than the brightest stable source known in these energies, the Crab Nebula. Thus, the GRB 190114C went on to hold the record of being the brightest known source of TeV photons. The emission faded rapidly over time, as did the post-luminescence already observed at lower energies. The last flashes were seen by MAGIC half an hour later.
For the first time, the MAGIC Collaboration announced the unequivocal detection of TeV photons from a GRB to the international astronomer community only a few hours after the alerts sent by the satellites, after careful verification of preliminary data. This facilitated an extensive campaign of observations in multiple wavelengths of the GRB 190114C, with the contribution of more than two dozen observatories and instruments, providing complete coverage of this GRB from the radio band to the TeV energies. In particular, the optical observations allowed measuring the distance that photons have traveled since they were generated in the GRB 190114C, approximately 4.5 billion light years.
Although the emission of TeV in the post-luminescence of GRBs had been predicted in some theoretical studies, it had never been experimentally confirmed, despite numerous efforts in recent decades with various instruments, including MAGIC. What physical mechanism is behind the production of the TeV photons finally detected by MAGIC? The energies are much higher than what can be expected from what is known as synchrotron radiation, caused by high-energy electrons moving within magnetic fields. This process is considered responsible for the emission that had previously been observed at lower energies in the post-luminescence of the GRB.
"The night we detected the GRB 190114C, I was in the control room of the MAGIC telescopes. From the first moment, we realized that the photons we were seeing passed the synchrotron radiation limit. These new results, along with the numerous data in multiple wavelengths, provide the first unequivocal evidence of an additional and distinct emission process in the post-luminescence, "explains Elena Moretti, astrophysics of the Spanish community and one of the main authors of the results. The analysis of the data indicates that the mechanism responsible for this emission is the so-called reverse Compton process, where electrons transfer energy by colliding with the population of existing photons, making them more energetic.
"After more than 50 years since the GRBs were discovered, many of its fundamental aspects remain a mystery," says Razmik Mirzoyan, the spokesperson for the MAGIC Collaboration. "The discovery of gamma ray emission in the GRB 190114C in the TeV band of the electromagnetic spectrum shows that GRBs are even more powerful than previously thought. The richness of the GRB 190114C data acquired by MAGIC and the extensive observations of Multi-wavelength tracking offers important clues to unravel some of the mysteries related to the physical processes that happen in GRBs. "
A comparative study of all previous GRB observations by MAGIC suggests that GRB 190114C was not a particularly unique event, except for its relative proximity (about 4.5 billion light years from Earth), and that successful detection is due to Excellent instrument performance. With the detection of the GRB 190114C, MAGIC opens a new window to study the GRB. Everything indicates that many more GRB can be detected in the energies of TeV and facilitate the way for a much deeper understanding of these fascinating cosmic explosions.
The Spanish community participates in MAGIC since its inception. Currently, MAGIC members are: the Center for Energy, Environmental and Technological Research (CIEMAT), the Institute of Astrophysics of the Canary Islands (IAC), the Institute of Physics d'Altes Energies (IFAE), the Autonomous University of Barcelona (UAB) , the Institute of Cosmos Sciences of the University of Barcelona (UB) and the Complutense University of Madrid (UCM). In addition, the MAGIC data center is the Port d'Informació Científica (PIC), a collaboration of IFAE and CIEMAT.
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