Speaker
Description
Summary
The energy flux of the excess component detected by IceCube is in agreement with predictions for neutrino emission from extragalactic jets in blazars and radio galaxies, based on the observation that a cosmologically evolving population of proton accelerators would produce similar calorimetric energy fluxes in gamma rays, protons, and neutrinos (Mannheim 1995). At neutrino energies between 100 TeV and 10 PeV, flat-spectrum radio quasars are expected to be the dominant source population, whereas BL Lac type blazars and radio galaxies are more important at higher or lower energies, respectively (Mannheim 2014). Proton acceleration within the broad-emission line region of quasars is limited by photo-hadronic energy losses due to interactions with ultraviolet photons from the near-Eddington accretion disk and scattered by the surrounding free electrons (Krauss et al. 2014). Subsequent pion decay releases PeV-scale neutrinos and gamma rays. The gamma rays are heavily degraded due to electromagnetic cascading in the low-energy radiation fields provided by the dust torus, spoiling the gamma-neutrino ratio from pion decay, but leaving calorimetric constraints intact. We study the probability of an association of blazars with the detected neutrino events, focusing on the most energetic of these events which have been detected with the greatest significance above the atmospheric background, and by using multi-frequency constraints to determine the calorimetric energy output of the objects during the IceCube exposure time. Taking into account that the resolved flat-spectrum radio quasars constitute only a fraction of the sources responsible for the extragalactic gamma-ray background, we find a satisfactory agreement between theory and observations.
