Neutrinos as a diagnostic of cosmic ray galactic-extragalactic transition

Motivated by a recent change in viewing the onset of the extragalactic component in the cosmic ray spectrum, we have fitted the observed data down to ${10}^{8.6}\text{ }\text{ }\mathrm{GeV}$ and have obtained the corresponding power emissivity. This transition energy is well below the threshold for resonant $p\ensuremath{\gamma}$ absorption on the cosmic microwave background, and thus source evolution is an essential ingredient in the fitting procedure. Two-parameter fits in the spectral and redshift evolution indices show that a standard Fermi ${E}_{i}^{\ensuremath{-}2}$ source spectrum is excluded at larger than 95% confidence level (CL). Armed with the primordial emissivity, we follow Waxman and Bahcall to derive the associated neutrino flux on the basis of optically thin sources. For $pp$ interactions as the generating mechanism, the neutrino flux exceeds the AMANDA-B10 90% CL upper limits. In the case of $p\ensuremath{\gamma}$ dominance, the flux is consistent with AMANDA-B10 data. In the new scenario the source neutrino flux is considerably enhanced, especially below ${10}^{9}\text{ }\text{ }\mathrm{GeV}$. Should data from AMANDA-II prove consistent with the model, we show that IceCube can measure the characteristic power law of the neutrino spectrum, and thus provide a window on the source dynamics.