Astrophysical implications of high energy neutrino limits I. Overall diffuse limits

Recently, improved quasi-isotropic limits to the diffuse extragalactic high energy neutrino component have been presented by AMANDA (Hill et al., 2006). In this paper, these limits will be discussed with respect to the consequences for various models of hadronic acceleration. Previous results showed that top-down scenarios explaining a possible proton flux above the Greisen-Zatsepin-Kuzmin (GZK) Cutoff could be excluded since these calculations result in an overproduction of neutrinos (Semikoz and Sigl, 2004). Here, we focus on neutrino production scenarios in different types of Active Galactic Nuclei (AGN). The new limits can exclude neutrino emission in correlation with X-ray emission from ROSAT detected AGN, which makes the Inverse Compton scenario for the X-ray emission more favorable. The implications of the limits to the neutrino flux from FR-II galaxies are discussed. It can be shown that current experimental limits to the quasi-isotropic neutrino flux give constraints to the optical depth of FR-II galaxies. Also, the special case of TeV blazars is examined. The general diffuse limit can be used to estimate the maximum contribution of photon-resolved TeV blazars to the total diffuse flux. It is shown that the observation of neutrinos is essential to get an understanding of high energy emission from extragalactic sources, since TeV photons only give a glance of the near Universe.