Simulated Radio Images and Light Curves of Young Supernovae

We present calculations of the radio emission from supernovae based on high-resolution simulations of the hydrodynamics and radiation transfer, using simple energy density relations that link the properties of the radiating electrons and the magnetic field to the hydrodynamics. As a specific example we model the emission from SN 1993J, which cannot be adequately fitted with the often-used analytic minishell model, and present a good fit to the radio evolution at a single frequency. Both free-free absorption and synchrotron self-absorption are needed to fit the light curve at early times, and a circumstellar density profile of ρ ~ r^-1.7 provides the best fit to the later data. We show that the interaction of density structures in the ejecta with the reverse supernova shock may produce features in the radio light curves such as have been observed. We discuss the use of high-resolution radio images of supernovae to distinguish between different absorption mechanisms and determine the origin of specific light curve features. Comparisons of VLBI images of SN 1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion. We predict that at 8.4 GHz the internal free-free absorption is currently declining, and that over the next ~40 yr the surface brightness of the center of the source should increase relative to the bright ring of emission seen in VLBI images. Similar absorption in a nearby supernova would make the detection of a radio pulsar at 1 GHz impossible for ~150 yr after explosion.