New theory for giant loops.

Four very large, shell-shaped features are known from the surveys of radio emission from the Galaxy. It is suggested that the giant loops represent a class of nebulae, induced by supernova radiation as opposed to supernova ejecta. The model considered provides a qualitative explanation for the spectral and polarization properties of the radio emission from giant loops. The radio emitting electrons are part of the general cosmic ray gas and need not arise specifically in the supernova that produced the fossil Stroemgren sphere.