Ponente
Descripción
The interactions of high-energy cosmic rays produce neutrinos and gamma rays. However, while neutrinos travel unimpeded, the accompanying gamma rays can trigger electromagnetic cascades via pair production on ambient photons, reprocessing their energy to lower frequencies. For intergalactic cascades produced in the propagation through extragalactic radiation, the resulting photons have a universal spectral shape, first described by Berezinsky in the 1970s. For internal cascades, developed within the astrophysical sources where the gamma rays are produced, the assumptions behind this result often break down due to dominant synchrotron losses. I will discuss a generalized theory of electromagnetic cascades, encompassing synchrotron-dominated cases, and determine the conditions under which a universal cascade spectrum can be obtained. I will focus on cascades triggered by gamma rays of hadronic origin and show how the universal spectrum emerges among a variety of high-energy astrophysical sources. These results are particularly relevant for predicting the electromagnetic counterpart of gamma-ray opaque sources, such as the coronae of active galactic nuclei, which are likely the dominant sources of the diffuse neutrino flux observed by the IceCube telescope.
