38 years of galactic observations in searching for neutrino bursts from core collapse supernovae with the Baksan Underground Scintillation Telescope

The core collapse of a massive star in the Milky Way will produce a neutrino burst, which will be detected by the Baksan Underground Scintillation Telescope (BUST). The stable and enough low background at the BUST is a clear asset for searching for neutrino bursts. Now two parts of the facility (with the total mass of 242 tons) are used as independent coinciding detectors. Such approach allows us to increase dependability detection of the neutrino signal and the radius of sensitivity of the BUST. The facility has the potential to see a supernova in the Galaxy independently from other detectors. No burst candidate for the core collapse has been detected during the observation period of June 30, 1980, to June 30, 2019. The actual observation time is 33.477 years. This is the longest observation time of our Galaxy with neutrinos at the same facility. An upper bound on the mean frequency of gravitational collapses in the Galaxy is 6.88 per century (at 90% C.L.).