Optical observations of nonthermal galactic radio sources

Abstract

A total of 9 nonthermal sources near the plane of the Galaxy have now been definitely identified with nebulosities. The identifications are well established; positions and sizes of the nebulosities and of the sources are in satisfactory agreement. At least three types of objects can be recognized: 1. Remnants of supernovae of type I. 2. The Cassiopeia A source, a remnant of a supernova of type II. 3. The Cygnus loop and several other large nebulosities which are most likely of similar origin. They also may be remnants of supernovae type II. The large size and the low surface brightness of these objects render their detailed investigation a difficult and time-consuming task. The true picture may emerge slowly, and conclusions drawn at an early stage of the work may have to be discarded as the investigation progresses.