Gamma ray is not a band with two edges. It is the open-ended top of the spectrum: everything above the x-rays, however high. From its doorstep near 100 keV to the most energetic photon ever caught, the gamma "band" spans about ten orders of magnitude, wider than every other named band combined. Drag the marker; tap a landmark.
Photon energy, 100 keV to 3 PeV
The hatched right end is where the extragalactic sky goes dark: a photon above ~100 TeV crossing intergalactic space collides with background starlight and becomes an electron–positron pair before it can arrive. And the attic does not stop at the record: between 1.4 PeV and the Planck energy lie thirteen more orders of magnitude in which no photon has ever been seen.
Nature's known accelerators, pulsar winds, supernova remnants, and the jets of feeding black holes, seem to top out near PeV photon energies. Above ~100 TeV the universe itself censors the view: over intergalactic distances, gamma rays annihilate against the cosmic background light. So the highest floors are structurally sound but unvisited: allowed by the physics, unreached by the sources, and hidden by the sky.
One PeV photon carries about the kinetic energy of a thrown ping-pong ball, packed into a single quantum of light.