ИСТИНА

MASTER Global Robotic Network of Lomonosov Moscow State University is the network of 8 robotic optical telescopes located all over the world. One of their goals is the search for optical counterparts to short- living transients such as GRB, gravitational waves and high-energy neutrinos. It is helped by the fast reaction time of the telescopes on such alerts and their fast slewing. On September 22, 2017 the neutrino observatory IceCube detected a high-energy astrophysical neutrino candidate that was connected to the flaring blazar TXS 0506+056, located in the neutrino error-box. MASTER-Tavrida telescope started the observations of the error-box 73s after the trigger time and was able to detect the blazar minutes after the trigger. We present the earliest astronomical observation of a high-energy neutrino error box of which the variability was discovered after high-energy-neutrino detection. MASTER found the blazar TXS 0506+056 to be in the off-state after one minute and then switched to the on-state no later than two hours after the event. The effect is observed at a 50σ significance level. We also present own a unique 16 yr light curve of blazar TXS 0506+056 (518 data set).