  Being primarily devoted to the physics interpretation, the talk starts with
the stereoscopic observation technique pioneered by HEGRA. The search for
Supernova Remnants is reviewed, the need for a consistent theory is argued, and
its elements are outlined. This theory is the basis for models regarding SN
1006 and Cas A. The analysis shows for the first time that emission spectra and
morphological detail are in agreement with the concept that these objects are
representative members of a suspected source population in the Galaxy. The
continuing study of this population is an essential part of the program of the
major new gamma-ray instruments.
