SYNCHROTRON EMISSION IN A RANDOM MAGNETIC-FIELD - THE EFFECT OF SPECTRAL AGING ON RADIO IMAGES

Images of radio synchrotron emission from volumes containing a random magnetic field have been constructed. The evolution of the images as the emission ages depends on the relative importance of synchrotron losses, inverse Compton losses and diffusion of electrons between regions of different field strength. The polarization from the volume can vary substantially with frequency as the result of differential ageing of polarized components, although this will not be important for sheared field configurations. Synchrotron ageing naturally increases the emission contrast at high frequencies, so that instabilities need not be invoked to explain the brightness of filamentary structures.