IceCube astrophysical neutrinos without a spectral cutoff and (10^15-10^17) eV cosmic gamma radiation

TL;DR

This paper analyzes IceCube neutrino data with unbroken power-law models, estimates associated gamma-ray fluxes, and discusses constraints from existing gamma-ray observations to understand the neutrinos' origins.

Contribution

It provides the first comprehensive analysis of unbroken power-law fits to IceCube neutrino data and explores gamma-ray flux predictions under different source scenarios.

Findings

Neutrino spectrum fits are consistent with unbroken power-laws at 68% confidence.

Gamma-ray flux estimates vary depending on source distribution and propagation effects.

Future gamma-ray observations could distinguish between Galactic and extragalactic neutrino sources.

Abstract

We present a range of unbroken power-law fits to the astrophysical-neutrino spectrum consistent with the most recent published IceCube data at the 68\% confidence level. Assuming that the neutrinos originate in decays of pi mesons, we estimate accompanying gamma-ray fluxes for various distributions of sources, taking propagation effects into account. We then briefly discuss existing experimental results constraining PeV to EeV diffuse gamma-ray flux and their systematic uncertainties. Several scenarios are marginally consistent both with the KASKADE and CASA-MIA upper limits at (10^15-10^16) eV and with the EAS-MSU tentative detection at ~10^17 eV, given large systematic errors of the measurements. Future searches for the diffuse gamma-ray background at sub-PeV to sub-EeV energies just below present upper limits will give a crucial diagnostic tool for distinguishing between the Galactic and extragalactic models of the origin of the IceCube events.