The Spectra of Opaque Radio Sources

Radio spectra are shown for thirty radio sources that show evidence of synchrotron self-absorption. As a result of inverse Compton cooling and adiabatic expansion, all opaque components have a maximum brightness temperature in the range 10h1_1012 ° K. The magnetic field deduced from the surface bright- ness and cutoff frequency in these sources is generally about 10-4±1 gauss. The variable components appear to have somewhat stronger magnetic fields