MHD SIMULATIONS OF RAYLEIGH-TAYLOR INSTABILITY IN YOUNG SUPERNOVA-REMNANTS

Radio observations shows that young supernova remnants such as Tycho a nd Cas A generally exhibit a circular clumpy shell. This shell shows a radial magnetic field whose equipartition strength is 2 to 3 orders o f magnitude higher than the interstellar field. A simple compression o f the ambient field by the shock can explain neither of these observat ions. We show that the Rayleigh-Taylor instability which occurs at the ejecta/ISM interface can explain these observations. We have done MHD simulations of the instability in the shell of Type-I supernova remna nts for the first time by utilizing moving grid technique. Our simulat ion shows that Rayleigh-Taylor and Kelvin-Helmholtz instabilities ampl ify ambient magnetic fields locally and produce the clumpy radio shell . Strong magnetic field lines draped around the Rayleigh-Taylor finger s produce the radial B-vector polarization, whereas thermal bremsstrah lung from the dense fingers themselves produce the clumpy X-ray emissi on.