Gamma-Ray Astronomy

Gamma-ray astronomy currently runs through an era of rapid progress and moving frontiers using satellite observatories up to photon energies of 10-to-100 GeV, and ground-based telescopes based on the imaging air-Cherenkov method. Such telescopes will soon be available for effective threshold energies above 10-to-50 GeV, therefore closing the last remaining gap in the coverage of the electromagnetic spectrum. Exploiting the non-thermal Universe,its relativistic particle content and the acceleration mechanisms operating in it, is a prime task of this field of research, but equally important is the potential of gamma-ray astronomy to probe the realm of heavy relic particles from the Early Universe, or to probe the propagation of energetic radiation across cosmological distances. (Author) 29 refs