Indication of a Local "Fog" of Sub-Ankle UHECR

Understand

During their propagation through intergalactic space, ultrahigh energy cosmic rays (UHECRs) interact with the background radiation fields.

• These interactions give rise to energetic electron/positron pairs and photons which in turn feed electromagnetic cascades, contributing to the isotropic gamma-ray background (IGRB).
• The gamma-ray flux level generated in this way highly depends upon the UHECR propagation distance, as well as the evolution of their sources with redshift.
• Recently, the Fermi-LAT collaboration reported that the majority of the total extragalactic gamma-ray flux originates from extragalactic point sources.