Institute for Advanced Study Informal Astrophysics Seminar

In 2012, the IceCube collaboration reported two PeV neutrino events. Then, 26 more events were found in a follow-up analysis.  Although more statistics are needed to have conclusive evidence, they are likely to include extraterrestrial signals.  In this talk, I will try to demystify the origin of this "IceCube excess". The current data suggest that high-energy neutrinos are produced inside astrophysical sources, while it is difficult to explain it with cosmogenic neutrinos.  I will also demonstrate the power of the multi-messenger approach.  It will be shown that present gamma-ray limits support extragalactic scenarios and further observations can test Galactic neutrino sources.  Any viable astrophysical scenario relies on pp or pgamma interaction as a neutrino production mechanism, and discriminating them is also relevant to reveal the sources. In particular, pp scenarios can be tested with multi-messenger data in the next several years.  I will discuss future prospects including implications of some specific pgamma scenarios.