1999ApJ...524L..91H

The recent detection of gamma radiation from Mrk 501 at energies as high as ∼25 TeV suggests stringent upper bounds on the diffuse, far-infrared, extragalactic radiation density. The production of electron-positron pairs through photon-photon collisions would prevent gamma photons of substantially higher energies from reaching us across distances of order 100 Mpc. However, coherently arriving TeV or sub-TeV gamma rays–Bose-Einstein condensations of photons at these energies–could mimic the Cerenkov shower signatures of extremely energetic gamma rays. To better understand such events, we describe their observational traits and discuss how they might be generated.