We here propose 3-night ToO observations to identify optical counterparts of IceCube high-energy cosmic neutrino sources. The origin of high-energy cosmic rays is decades-long mystery in astrophysics. Cosmic rays produce high-energy neutrinos via hadronic interactions, and identification of cosmic-neutrino sources provides a smoking-gun evidence of the cosmic-ray origin. Previous studies indicate that tidal disruption events (TDEs) are the most promising candidate of the cosmic-neutrino sources. The expected apparent magnitude to a neutrino emitting TDE is r∼21−25 mag as the majority should be at high redshift, and the error circle radius of a neutrino event is around 0.7 deg. Thus, a deep and wide survey is necessary to identify neutrino counterpart, which is possible only by Subaru/HSC. We search for a distant TDE candidate when a high-quality IceCube alert is issued. We can distinguish a distant TDE from unrelated supernovae using their lightcurve and color evolution. We will also perform Gemini/GMOS spectroscopic observation to characterize the candidate TDE and its host galaxy. The proposed observations will enable us to establish TDEs as the dominant source of cosmic neutrinos, or strongly rule out TDEs as their sources if no TDE is discovered.
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