Development of an IceCube Realtime Alert using Multiplet Signal for Optical Follow-Up

Multi-messenger observation of neutrino sources is a key for identifying the origin of astrophysical neutrinos, and it led to the identification of the blazar TXS 0506+056 as the first candidate in 2017. When the IceCube observatory detects neutrino signals, alerts are sent to the other telescopes to trigger follow up observations. The newly proposed algorithm tries to find long time scale doublets and triplets, where two or three astrophysical neutrino event candidates are observed from the same direction within 30 days. This signature selects neutrino sources close to our galaxy, and makes it easier to do the follow up observation by optical telescopes. Utilizing the 11 years archival data, the signal extraction efficiencies of time and spatial clustering algorithms were evaluated, and found that the new method showed significantly better performance for small number of detected events. Finally, the sensitivity of the new alert channel is presented in the phase space of neutrino source model parameters.