The IceCube Neutrino Observatory has detected a flux of 1-10 \, TeV neutrinos from the active galaxy, NGC 1068. The soft spectral index of these neutrinos has previously been interpreted as an indication that this source accelerates protons only up to energies of several hundred TeV. Here, we propose that this source might instead accelerate protons to significantly higher energies, but that the charged pions and muons produced in their interactions undergo significant synchrotron energy losses before they can decay, leading to a cutoff in the neutrino spectrum at TeV-scale energies. This scenario would require very strong magnetic fields to be present in the acceleration region of NGC 1068, on the order of B 10⁷ \, G. We point out that this synchrotron cooling would impact the flavor ratios of the neutrinos from this source, providing a means to test this scenario with future very-large volume neutrino telescopes.
Blanco et al. (Thu,) studied this question.