Neutrino-Shining Coronae in Active Galactic Nuclei: Radiative Signatures and Insights into Particle Acceleration
The emergence of the Seyfert galaxy NGC 1068 as the most significant source of high-energy astrophysical neutrinos observed by IceCube marked a turning point in our understanding of the neutrino sky. This neutrino signal implies the presence of hadronic acceleration to up to 100 TeV-PeV energies. Furthermore, as neutrino production is expected to be accompanied by electromagnetic radiation of similar energies, the lack of observation of TeV gamma-rays strongly hints at the existence of a radiatively compact emission region of neutrinos, where the accompanying photons are absorbed and reprocessed at lower energies starting an electromagnetic cascade. For active galactic nuclei (AGN), the hot X-ray corona in the vicinity of the central supermassive black hole is a natural candidate for this opaque, highly energetic environment.
In this talk, I will review the current understanding of neutrino emission from AGN coronae, focusing on two scenarios of non-thermal particle acceleration that successfully explained the neutrino signal of NGC 1068: acceleration in magnetic reconnection and turbulence. I will show how the multimessenger signals observed from sources like NGC 1068, within the framework of turbulent acceleration, favor a compact, strongly magnetized, and highly turbulent coronal environment. Furthermore, I will demonstrate how high radiative compactness and intense magnetic fields constrain the spectral shape of the reprocessed electromagnetic radiation, forcing the internal cascade into a universal spectral shape. Finally, I will discuss how applying these coronal models to jetted sources, such as the blazar TXS 0506+056, fails to explain their observed neutrino flux, highlighting how the production of neutrinos could happen simultaneously in different regions of the AGN, but suggesting that in blazars the most luminous emission region is located in the jet.
