It is a real delight and honor to realize that some unparalleled and unique discoveries made today at world-famous institutions, to a certain extent have their roots Yerevan Physics Institute (YerPhI), now Alikhanian National Laboratory (AANL), sparked by Armenian physicists. One of these phenomena is the discovery of gamma-ray bursts and the highest-energy photons measured from these objects.
Back in the 1980s Cosmic Ray Division of YerPhI (AANL) in collaboration with Lebedev Physical Institute, Moscow were preparing the world-largest cosmic ray experiment named ANI on Aragats. Within the framework of the project, it was planned to employ various particle detectors, including the technique of arrays of imaging atmospheric Cherenkov telescopes (IACTs) to register very high energy gamma rays from stellar point sources. However, the collapse of the Soviet Union halted the construction, and the two leading scientists, Felix Aharonyan and Razmik Mirzoyan moved from Yerevan Physics Institute (now AANL) to Germany. With colleagues from Max Planck Institutes in Munich and Heidelberg, Armenian physicists launched the first system of European ACTs on La Palma, Canary Islands (HEGRA). The success and efficiency of the IACT technique along with the Armenian Armenian design triggered further collaborations. As a result, larger telescopes were commissioned on La Palma (MAGIC) and in Namibia (H.E.S.S.). Still, at YerPhI (AANL), particularly at CRD and Aragats Station, the scientific work in this direction was swiftly unfolding. Hence, advanced methods of gamma image selection based on machine learning algorithms were developed by Professor Ashot Chilingarian and for the first time applied to IACT data analysis.
Currently Armenian physicists participate both in MAGIC and H.E.S.S. collaborations. Recently a group of younger Armenian astrophysicists from International Center for Relativistic Astrophysics Network (ICRANet-Armenia) has joined MAGIC. At present, the activities of the international collaboration are directed towards the Cherenkov Telescope Array (CTA) project with about a hundred IACTs to exceed and the capabilities of the existing telescopes. These developments enabled the exciting results in the field of high-energy astrophysics and the recent detection of the first gamma-ray bursts (GRBs) by the MAGIC telescopes, known as GRB 190114C, to reveal for the first time the highest-energy photons measured from these objects. This ground-breaking achievement by MAGIC provides critical new insight to understand the physical processes at work in GRBs, which are still mysterious.
On January 14, 2019, a GRB was discovered independently by two space satellites: the Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope. The analysis of the resulting data for the first tens of seconds reveals emission of photons in the afterglow reaching teraelectronvolt (TeV) energies, that is, a million million(1012) times more energetic than visible light, and still a million times more energetic than the gamma rays through which GRBs are detected in satellite detectors. During this time, the emission of TeV photons from GRB 190114C was 100 times more intense than the brightest known steady source at TeV energies, the Crab Nebula. In this way, GRB 190114C became the record-setter as the brightest known source of TeV photons. An extensive campaign of multi-wavelength (MWL) follow-up observations of GRB 190114C ensued by over two dozen observatories and instruments, providing a full observational picture of this GRB from the radio band to TeV energies. In particular, optical observations made a measurement of the distance to GRB 190114C. It was found that this GRB is located in a galaxy from which it took 4.5 billion years for the light to reach the Earth.
"After more than 50 years since GRBs were first discovered, many of their fundamental aspects still remain mysterious", says RazmikMirzoyan, the Spokesperson of the MAGIC Collaboration. "The discovery of gamma-ray emission from GRB 190114C in the new, TeV window of the electromagnetic spectrum shows that the GRB explosions are even more powerful than thought before. The wealth of new data on GRB 190114C acquired by MAGIC offers important clues to unravel some of the mysteries concerning the physical processes at work in GRBs". Two papers in the Nature issue of November 21 describe the detection of the gamma rays up to TeV energies with MAGIC and the indication that inverse Compton scattering is the responsible process at work. A third paper in the same issue describes the detection of another gamma ray burst with energies above 100 GeV (but below 1 TeV) from GRB 180720B, using the High Energy Stereoscopic System (H.E.S.S.) array of telescopes in Namibia. Although these photons were lower in energy and fewer in number than those observed from GRB 190114C, they were detected from deep in the afterglow phase (10 hours after the GRB was triggered).
All these fascinating results were realized based on important contributions of Armenian physicists. Three papers in the same issue of Nature confirm the exceptional nature of the results obtained, of which the gamma-ray community, including Armenia, could be proud of.
Papers in Nature
Nature volume 575: 455-458 (2019). https://www.nature.com/articles/s41586-019-1750-x