Neutrinos, Cosmic Rays and the MeV Band

Understand

The possible association of the blazar TXS 0506+056 with a high-energy neutrino detected by IceCube holds the tantalizing potential to answer three astrophysical questions: 1.

• Where do high-energy neutrinos originate? 2.
• Where are cosmic rays produced and accelerated? 3.
• What radiation mechanisms produce the high-energy {\gamma}-rays in blazars? The MeV gamma-ray band holds the key to these questions, because it is an excellent proxy for photo-hadronic processes in blazar jets, which also produce neutrino counterparts.