Multimessenger View of High-Energy Cosmic Neutrino Sources

The discovery of high-energy cosmic neutrinos opened a new window of astroparticle physics. Their origin is a new mystery in the field, which is tightly connected to the long-standing puzzle about the origin of cosmic rays. I will discuss theoretical implications of the latest results on high-energy neutrino observations, and demonstrate the power of multi-messenger approaches. I will highlight our recent developments about astrophysical neutrino emission from gamma-ray dark sources, including the obscured active galactic nucleus NGC 1068, as well as violent transient phenomena such as supermassive black hole flares.