On interpretations of observed radio properties of CAS A

Cas A, which is probably the youngest (less than about 300 yr) galactic supernova remnant, is examined in terms of the secular decay in brightness and the asymmetry of the shell. Bell's (1977) observations linking these two aspects of the evolution of Cas A are considered, in which differences in the secular change of individual features have been recognized. With regard to the asymmetry of Cas A, it is noted that the brighter side is nearer to the galactic plane; the secular variation of the brightness gradient is also considered. In addition, the decay problem, the evolution of the radio spectrum, and the magnetic field of Cas A are discussed.