2025ApJ...993...23T

Optical transients with timescales of months, such as supernovae (SNe) and tidal disruption events (TDEs), are candidates for high-energy neutrino sources. Multiple neutrino detections from the same direction within a month timescale provide a unique opportunity to identify such optical counterparts in the nearby Universe. In this work, we conduct an archival search for the optical counterpart of an IceCube triplet event using the data of Zwicky Transient Facility. We develop a dedicated alert filtering system and validate the performance by following a blind analysis method. Applying this filtering system to the data after the detections of the IceCube triplet event, we find no transient candidates within the localization area. Assuming that the IceCube triplet event originates from an astrophysical source, we constrain parameters of the optical transient, a peak luminosity, and a decay timescale, using a simple signal model that is motivated by TDEs and superluminous SNe (SLSNe). For the case with no time lag between neutrino detections and optical peak, almost the entire parameter space of the known TDEs and SLSNe would be constrained. To give constraints on transients with a rapidly evolving light curve, quick follow-up observations for future neutrino multiplet events are crucial.