Twenty Years of Galactic Observations in Searching for Bursts of   Collapse Neutrinos with the Baksan Underground Scintillation Telescope
  The results of twenty-year-long Galactic observations in neutrino radiation are summarized. Except for the recording of a neutrino signal from the supernova SN 1987A, no Galactic bursts of collapse neutrinos have been detected. An upper bound on the mean frequency of gravitational collapses in our Galaxy was obtained, $f_{collapse} (90% {confidence}) < 0.13 {yr}^{-1}$. 
E.N.Alexeyev, L.N.Alexeyeva (Institute for Nuclear Research, Russian   Academy of Sciences)