Limits on the source properties of FR-I galaxies from high-energy neutrino and gamma observations

Active galactic nuclei (AGN) are believed to be the source of ultra high energy cosmic rays (UHECRs, E>1018eV). Particles are assumed to be accelerated in the accretion disk and the plasma jets, produced due to conservation of angular momentum, to the highest energies, where they interact with each other and produce pions, which decay among others in neutrinos.For a known cosmic ray (CR) spectral behavior, the main parameters in the calculation of the neutrino flux from proton–proton (p–p) interactions are the target density nHnH and the ratio of electrons to protons fefe. Using most recent neutrino flux limits from IceCube point source searches, we set limits on the target densities for 33 FR-I galaxies. The densities are shown to be smaller than 30 cm-3cm-3 to 2·103cm-3, depending on the source and when using a fixed electron to proton ratio of fe=0.1fe=0.1. This implies that some CR acceleration sites, especially those close to the core of the AGN, can already be excluded, or else that the ratio of electrons to protons deviates significantly from the commonly used value of 0.1.For Centaurus A (Cen A) and Messier 87 (M 87) we use Fermi observations to model the γγ-flux, the neutrino flux and the resulting target density. The detection of these neutrinos will help to find information about acceleration processes in the source.