KASCADE-Grande Limits on the Isotropic Diffuse Gamma-Ray Flux between 100 TeV and 1 EeV

TL;DR

This paper establishes upper limits on the flux of isotropic diffuse gamma-rays in the 100 TeV to 1 EeV range using data from KASCADE and KASCADE-Grande, constraining astrophysical models of gamma-ray sources.

Contribution

It provides the first comprehensive upper limits on gamma-ray flux in the 10^14 to 10^18 eV range based on air shower data, improving constraints on high-energy gamma-ray origins.

Findings

Set 90% C.L. upper limits on gamma-ray flux between 10^14 and 10^18 eV.

Achieved the best upper limit at 3.7×10^15 eV with a gamma-ray fraction of 1.1×10^-5.

Constrained models of astrophysical sources, including IceCube neutrino source models.

Abstract

KASCADE and KASCADE-Grande were multi-detector installations to measure individual air showers of cosmic rays at ultra-high energy. Based on data sets measured by KASCADE and KASCADE-Grande, 90% C.L. upper limits to the flux of gamma-rays in the primary cosmic ray flux are determined in an energy range of ${10}^{14} - {10}^{18}$ eV. The analysis is performed by selecting air showers with a low muon content as expected for gamma-ray-induced showers compared to air showers induced by energetic nuclei. The best upper limit of the fraction of gamma-rays to the total cosmic ray flux is obtained at $3.7 \times {10}^{15}$ eV with $1.1 \times {10}^{-5}$. Translated to an absolute gamma-ray flux this sets constraints on some fundamental astrophysical models, such as the distance of sources for at least one of the IceCube neutrino excess models.