MODEL IMAGES OF RADIO HALOS AROUND SUPERNOVA-REMNANTS

I present model calculations of profiles and two-dimensional images of the radio synchrotron emission of young supernova remnants, concentra ting on observable effects of relativistic electrons diffusing upstrea m of the shock wave. If the preshock electron scattering mean free pat h is sufficiently long, observable synchrotron halos outside the bulk of the radio emission can potentially result; their absence can constr ain the mean free path from above. If scattering is primarily due, as expected, to Alfven waves with amplitude delta B, the halo is expected to extend a distance of order r(g)c(delta B/B)(-2)/v(s) beyond the sh ock, where r(g) is the gyroradius of the electrons emitting at the obs erved frequency, B is the upstream magnetic field strength, v(s) is th e shock velocity, and the amplitude delta B refers to waves with wavel ength comparable to r(g), of order 10(13) cm for typical supernova-rem nant parameters. However, the detailed geometry of the halo varies wit h the assumptions about particle acceleration in the shock wave. I pre sent an atlas of model profiles and images as a function of preshock d iffusion length, of aspect angle between the magnetic field and the li ne of sight, and of other relevant parameters.