Einstein and Plank would scorn you for calling them Gamma Rays 
I just linked the article but come to think of it Astronomers call the mysterious deep space events Gamma Ray bursts.
From a nuclear perspective gamma and X-ray are clearly described by source, what happens when the source is unknown? Quasar streams would seem to fit X-Ray but pulses from Super Novas are the decay of a star with much of it from fusion that would seem to fit gamma rays. Perhaps Gamma is becoming the "Klennex" of the high energy photon world.
