The H.E.S.S. Gamma ray observatory in the Namibian desert has sufficient collecting area that it is able to detect very rare high energy that were simply not available to space observatories with comparatively low collecting areas.
H.E.S.S. detects high energy gamma rays from all sorts of astrophysical objects and processes. A non-comprehensive lsit would include Supernovae, pulsars, starburst galaxies and active galactic nuclei as well as some gamma rays with no obvious counterpart.
For a brief scan of the gamma ray spectra of some of the objects observed it appears that gamma rays with energies of up to 100 TeV are routinely collected. Most spectra seem to follow a declining power law at high energies, so there will be higher energy gamma rays, they are just to rare that they are not being found.