PeV neutrinos observed by IceCube from cores of active galactic nuclei

Recently, the IceCube Collaboration has reported the first observation of cosmic 2 PeV energy neutrinos giving a signal 3 above the atmospheric background [1]. More recently, 18 events 4 above the expected atmospheric background were reported with energies above 100 TeV. These neutrinos are likely to be of cosmic origin; their angular distribution is consistent with isotropy. The average spectral index for these neutrinos was approximately 2 over the energy range between 100 TeV and 2 PeV [2]. In 1991 we proposed a model suggesting that very high energy neutrinos could be produced in the cores of active galaxies (AGN) such as Seyfert galaxies [3]. Using that model, we gave estimates of the flux and spectrum of high energy neutrinos to be expected. In light of subsequent AGN observations and the discovery of neutrino oscillations, the flux estimates for this model were revised downward [4], although the shape of the predicted neutrino spectrum remained unchanged. The new estimate was obtained by lowering the flux shown in the figure in Ref. [5] by a factor of 20. This rescaling gives a value for the flux at 100 TeV of E ðE Þ 10 8 GeV cm 2 s 1 sr 1 and a flux of 5:6 10 8 GeV cm 2 s 1 sr 1 at 1 PeV. The peak flux in these units occurs at an energy 1 PeV. In our model protons are accelerated by shocks in the cores of AGN in the vicinity of the black hole accretion disk (see, e.g., Ref. [6]). Being trapped by the magnetic field, they lose energy dramatically by interactions with the dense photon field of the ‘‘big blue bump’’ of thermal emission from the accretion disk (see, e.g., Ref. [7]) which is optically thick to protons [3]. The primary interactions are those from photomeson production. The primary neutrino producing channel, which occurs near threshold, is þ p ! þ ! nþ þ; (1)