Photohadronic Origin of the TeV-PeV Neutrinos Observed in IceCube

TL;DR

This paper investigates the origin of IceCube's high-energy neutrinos, suggesting they are produced by photohadronic interactions in astrophysical sources with strong magnetic fields, and uses spectral and flavor data to constrain source models.

Contribution

It introduces a method to identify neutrino sources based on spectral shape and flavor composition, considering magnetic field effects, and constrains source classes with current and future IceCube data.

Findings

Sources with strong magnetic fields are favored due to lack of ultra-high energy neutrinos.

Simple AGN models can explain current data at about 3sigma confidence.

Future data could exclude sources of ultra-high energy cosmic rays at over 5sigma.

Abstract

We perform an unbiased search of the origin of the recently observed 28 events above ~30 TeV in the IceCube neutrino observatory, assuming that these are (apart from the atmospheric background) of astrophysical origin produced by photohadronic interactions. Instead of relying on the normalization of the neutrino flux, we demonstrate that spectral shape and flavor composition can be used to constrain or identify the source class. In order to quantify our observations, we use a model where the target photons are produced by the synchrotron emission of co-accelerated electrons, and we include magnetic field effects on the secondary muons, pions, and kaons. We find that the lack of observed events with energies much larger than PeV points towards sources with strong magnetic fields, which do not exhibit a direct correlation between highest cosmic ray and neutrino energies. While the simplest AGN models with efficient proton acceleration plausibly describe the current data at about the 3sigma confidence level, we show that IceCube can rule out that the observed neutrinos stem from the sources of the ultra-high energy cosmic rays with a factor of ten increased statistics at more than 5sigma if the current observations are confirmed. A possible caveat are sources with strong magnetic fields and high Lorentz factors, such as magnetic energy dominated GRBs.