Very recently the IceCube Collaboration has reported an observation of 28 neutrino candidates with energies between 50 TeV and 2 PeV, constituting a $4.1\sigma$ excess compared to the atmospheric background. In this article we investigate the compatibility between the data and a hypothesized unbroken power-law neutrino spectrum for various values of spectral index $\mathrm{\Gamma }\ge 2$. We show that $\mathrm{\Gamma }\sim 2.3$ is consistent at the $\sim 1.5\sigma$ level with the observed events up to 2 PeV and to the null observation of events at higher energies. We then assume that the sources of this unbroken spectrum are Galactic, and deduce (i) an energy-transfer fraction from parent protons to pions (finding ${\epsilon }_{{\pi }^{\pm }}$ and ${\epsilon }_{\pi }$), and (ii) a way of discriminating among models which have been put forth to explain the “knee” and “ankle” features of the cosmic ray spectrum. Future IceCube data will test the unbroken power-law hypothesis and provide a multimessenger approach to explaining features of the cosmic ray spectrum, including the transition from Galactic to extragalactic dominance.

• Received 28 June 2013

DOI:https://doi.org/10.1103/PhysRevD.89.083003