Search for transient sources of high-energy neutrinos with IceCube: tests of the real-time analysis

The astrophysical sources of neutrinos with energy above GeV are to date unknown. A discovery of these objects would provide a smoking gun signature of the unknown cosmic rays sources, since their production is correlated. In addition, neutrinos are a unique tool to probe the most extreme environments in our Universe: their interaction cross section is low and they are electrically neutral, allowing them to travel undeflected and almost unabsorbed. The IceCube detector, located at the South Pole, observes neutrinos in the energy range from TeV to PeV. Real-time analyses process the IceCube data in order to rapidly identify signal neutrinos, sending alerts to the astrophysical community for follow-up observations in case of interesting results. Two of them are relevant for this work, both searching for signal neutrino clusters from individual sources: one monitors known transient gamma-ray sources, the other performs an unbiased all-sky search. This work focuses on testing the core algorithm of these real-time analyses. Neutrino clusters from point-like sources, characterised by number of signal neutrinos, flux spectral index and flare duration, are simulated for sources in different positions in the sky. The reconstruction quality of the cluster parameters is studied, highlighting the behaviour of the algorithm for different simulation conditions. The discovery potential, i.e. the flux that yields a 5σ discovery in 50% of the cases, is also evaluated for every simulated source. Finally, the possibility to identify sources emitting neutrinos during time scales shorter than few hours is discussed.