Neutrinos from active galactic nuclei as a diagnostic tool

Abstract

Active galactic nuclei (AGN) are known as sources of high energy γ -rays. The emission probably results from non-thermal radiation of relativistic jets belonging to the AGN. Earlier investigations of these processes have suggested that neutrinos are among the radiation products of the jets and may be used to discriminate between hadrons and leptons as primary particles for the production of the high energy emission. Our calculation of the high energy neutrino emission from the jets of AGN is based on a recently published model for γ -ray production by a collimated, relativistic blast wave, in which the spectral evolution of energetic particles is determined by the interplay between the particle injection by sweep-up of the interstellar medium, the energy losses through radiation, and diffusive escape. It is important to note that the swept-up interstellar particles retain their relative velocities with respect to the jet plasma, but get isotropised in the jet rest frame by self-excited $\rm Alfv\acute{e}nic$ turbulence. The bulk of the neutrino emission is expected in the energy range between 100 GeV and a few TeV. It is shown that the neutrino flux is correlated with the flux of TeV γ -rays. This allows to distinctly search for neutrino emissions from the jets of AGN by using the TeV γ -ray light curves to drastically reduce the temporal and spatial parameter space. Given the observed TeV photon fluxes from nearby BL Lacs the neutrino signal from AGN may be detectable with future neutrino observatories as least as sensitive as IceCube.