ON THE RECENT DETECTIONS OF GAMMA-RAY BURSTS AT TERAELECTRONVOLT ENERGIES

Razmik Mirzoyan – Max-Planck Institute for Physics

A quarter of century ago the MAGIC telescope project defined its goal to extend the observational energy range of very high energy gamma rays by using the ground-based imaging air Cherenkov technique from a few hundred down to few tens of GeV. Closing the order of magnitude energy gap between the satellite and ground-based observational techniques and providing real-time high-detection rates of gamma-rays from diverse celestial sources as, for example, from pulsars, distant active galactic nuclei and gamma-ray bursts (GRBs), was considered of key importance. The telescopes were designed to receive satellite alerts and automatically re-position within 20-25 seconds and observe any chosen type of source at any given position in the sky. Most of these design features were implemented in the hope to measure TeV gamma-rays from GRBs, hopefully still in the prompt emission phase. With time we learnt to further enhance the sensitivity of the telescopes and measure sources as in the few tens of GeV as well as at a few hundred TeVs. Similar preparations were met by the other ground-based TeV facilities, but still the GRB hunt remained elusive. Finally, after ~15 years of operating MAGIC we succeeded measuring a 50 σ gigantic signal from GRB 190114C at redshift 0.42 at energies (0.2 – 2) TeV in the afterglow phase, starting one minute after onset of the GRB. This was followed by the measurement of GRB 180720B at redshift 0.65, 10h after the onset and announcement of GRB190829A at redshift 0.079 by H.E.S.S., 4 h after the onset. A couple of weeks ago MAGIC sent a GCN circular with a hint from GRB201015A at redshift 0.43. The very young family of GRBs at TeV keeps expanding and taking shape. It helps us to reveal significant novel features and exciting results about the most powerful sources of electromagnetic radiation in the Universe and the space-time.