  Auger results on clustering of > 60 EeV ultra-high energy cosmic ray (UHECR)
ions and the interpretation of the gamma-ray spectra of TeV blazars are
connected by effects from the extragalactic background light (EBL). The EBL
acts as an obscuring medium for gamma rays and a reprocessing medium for UHECR
ions and protons, causing the GZK cutoff. The study of the physics underlying
the coincidence between the GZK energy and the clustering energy of UHECR ions
favors a composition of > 60 EeV UHECRs in CNO group nucleons. This has
interesting implications for the sources of UHECRs. We also comment on the
Auger analysis.
