Cosmic gamma-ray bursts and soft gamma-repeaters — observations and modeling of extreme astrophysical phenomena (100th anniversary of the Ioffe Institute)

Cosmic gamma-ray bursts (GRBs) and soft gamma-ray repeaters (SGRs) are the brightest sources of high-energy electromagnetic radiation. For many years, GRB and SGR studies have been among the major basic research areas at the Ioffe Institute. The physical processes that power immense luminosity of the cosmic gamma-ray sources are of utmost interest because they enable exploring physical phenomena in the vicinities of stellar-mass black holes and neutron stars, whose magnetic fields are probably larger than the critical vacuum polarization value, i.e., under conditions inaccessible in terrestrial laboratories. Owing to the high luminosity, GRBs can be detected at distances up to the edge of the visible Universe, and thus enable studying how the first stars emerged and probing the properties of matter along the entire line of sight to the sources. We briefly review the results of modern multi-wavelength studies of cosmic GRBs and SGRs. We discuss the history of the GRBs and SGRs studies, a vibrant area of basic astrophysical research at the Ioffe Institute, their accomplishments and prospects. We describe in detail the results obtained with several generations of KONUS detectors that have been designed and manufactured at the Ioffe Institute. Observational data obtained by space-based instruments are effectively complemented by theoretical modeling of astrophysical processes that exhibit extreme energy release. We also discuss prospects for GRB and SGR studies, including future experiments scheduled at the Ioffe Institute.