Estimates of the cosmic gamma-ray flux at PeV to EeV energies from the EAS-MSU experiment data

TL;DR

This paper analyzes archival EAS-MSU data to detect and constrain the flux of cosmic gamma rays in the PeV to EeV energy range, confirming previous findings and providing new upper limits in previously unexplored energies.

Contribution

It refines the analysis of EAS-MSU data to confirm gamma-ray flux detection and establishes the first constraints in the 10^17-10^18 eV range.

Findings

Confirmed gamma-ray flux at ~5x10^16 eV with similar flux value

Provided upper limits on gamma-ray flux below and above this energy

First constraints established in the 10^17-10^18 eV energy range

Abstract

Archival EAS-MSU data are searched for anomalous muonless events which may be caused by primary gamma rays with energies between 10^15 eV and 10^18 eV. We consider a refined sample of high-quality data and confirm the previously reported detection of a non-zero gamma-ray flux at ~5x10^16 eV with a similar flux value but at somewhat lower statistical significance, corresponding to the depletion of the sample. We present upper limits on the flux below and above these energies, including the first constraints in the range (10^17-10^18) eV never studied by any other experiment.