The TeV Diffuse Cosmic Neutrino Spectrum and the Nature of Astrophysical Neutrino Sources

TL;DR

This paper analyzes the TeV to PeV diffuse cosmic neutrino flux measured by IceCube, revealing insights into the nature of astrophysical sources, especially those obscured in gamma rays, and constraining their radiation environments.

Contribution

It provides a model-independent characterization of the low-energy neutrino flux, linking it to gamma-ray-obscured sources and their radiation fields, based on existing data.

Findings

Neutrinos likely originate from gamma-ray-obscured cosmic environments.

Cascaded gamma-ray flux from sources may contribute to the diffuse MeV-GeV background.

Constraints on source radiation fields are derived from gamma-ray background observations.

Abstract

The diffuse flux of cosmic neutrinos has been measured by the IceCube Observatory from TeV to PeV energies. We show that an improved characterization of this flux at the lower energies, TeV and sub-TeV, reveals important information on the nature of the astrophysical neutrino sources in a model-independent way. Most significantly, it could confirm the present indications that neutrinos originate in cosmic environments that are optically thick to GeV-TeV $\gamma$-rays. This conclusion will become inevitable if a steeper or even uninterrupted neutrino power law is observed in the TeV region. In such $\gamma$-ray-obscured sources, the $\gamma$-rays that inevitably accompany cosmic neutrinos will cascade down to MeV-GeV energies. The requirement that the cascaded $\gamma$-ray flux accompanying cosmic neutrinos should not exceed the observed diffuse $\gamma$-ray background, puts constraints on the peak energy and density of the radiation fields in the sources. Our calculations inspired by the existing data suggest that a fraction of the observed diffuse MeV-GeV $\gamma$-ray background may be contributed by neutrino sources with intense radiation fields that obscure the high-energy $\gamma$-ray emission accompanying the neutrinos.