Energetics of High-Energy Cosmic Radiations

TL;DR

This paper investigates the energy densities of high-energy cosmic radiations, exploring their connections through neutrino and gamma-ray observations, and discusses potential sources and acceleration mechanisms for these cosmic rays.

Contribution

It provides a detailed analysis of cosmic-ray spectra and their compatibility with neutrino and gamma-ray data, proposing scenarios involving reacceleration or extragalactic sources with hard spectra.

Findings

A power-law index of ~2.1-2.2 fits the ultrahigh-energy component.

Extrapolated GeV-TeV spectra can match PeV neutrino data but overpredict gamma-ray luminosity.

Hard spectra at ultrahigh energies can be consistent with both neutrino and gamma-ray observations.

Abstract

The luminosity densities of high-energy cosmic radiations are studied to find connections among the various components, including high-energy neutrinos measured with IceCube and gamma rays with the Fermi satellite. Matching the cosmic-ray energy generation rate density in a GeV-TeV range estimated for Milky Way with the ultrahigh-energy component requires a power-law index of the spectrum, $s_{\rm cr}\approx2.1-2.2$, somewhat harder than $s_{\rm cr}\approx2.3-2.4$ for the local index derived from the AMS-02 experiment. The soft GeV-TeV cosmic-ray spectrum extrapolated to higher energies can be compatible with PeV cosmic rays inferred from neutrino measurements, but overshoots the CR luminosity density to explain GeV-TeV gamma rays. The extrapolation from ultrahigh energies with a hard spectrum, on the other hand, can be consistent with both neutrinos and gamma-rays. These point towards either reacceleration of galactic cosmic rays or the presence of extragalactic sources with a hard spectrum. We discuss possible cosmic-ray sources that can be added.