Upper limit on the diffuse extragalactic radio background from GZK photon observation

TL;DR

This paper proposes that observing GZK photons from ultra-high-energy cosmic rays can set an upper limit on the extragalactic radio background, updating previous flux predictions and linking to future cosmic ray data.

Contribution

It introduces a method to constrain the extragalactic radio background using GZK photon observations and updates flux predictions based on proton primary models.

Findings

GZK photon fluxes depend on UHECR proton composition.

Observation of GZK photons can limit the extragalactic radio background.

Updated flux predictions for GZK photons from proton primaries.

Abstract

Here we point out that an observation of Ultra-High Energy Cosmic Ray (UHECR) photons, "GZK photons", could provide an upper limit on the level of the Extra-Galactic Radio Background, depending on the level of UHECR proton primaries (to be determined after a few years of data taking by the Pierre Auger Observatory upgrade AugerPrime). We also update our 2005 prediction of the range of GZK photon fluxes expected from proton primaries.