Radio Emission from a Young Supernova Remnant Interacting with an Interstellar Cloud: Magnetohydrodynamic Simulation with Relativistic Electrons

We present two-dimensional MHD simulations of the evolution of a young TypeIa supernova remnant during its interaction with an interstellar cloud ofcomparable size at impact. We include for the first time in such simulationsexplicit relativistic electron transport, including spectral information usinga simple but effective scheme that follows their acceleration at shocks andsubsequent transport. From this information we also model radio synchrotronemission, including spectra. The principal conclusions from these experimentsare: 1) Independent of the cloud interaction, the SNR reverse shock can be anefficient site for particle acceleration in a young SNR. 2) At these earlytimes the synchrotron spectral index due to electrons accelerated at theprimary shocks should be close to 0.5 unless those shocks are modified bycosmic-ray pressures. However, interaction with the cloud generates regions ofdistinctly steeper spectra, which may complicate interpretation in terms ofglobal dynamical models for SNR evolution. 3) The internal motions within theSNR become highly turbulent following the cloud interaction. 4) An initiallyuniform interstellar magnetic field is preferentially amplified along themagnetic equator of the SNR, primarily due to biased amplification byinstabilities. Independent of the external field configuration, there is a netradial direction to this field inside the SNR. 5) Filamentary radio structurescorrelate well with magnetic filaments, while diffuse emission follows theelectron distribution. 6) Interaction with the cloud enhances both the electronpopulation and the radio emission.Comment: 29 pages of Latex generated text with 6 figures in gif format. Accepted for publication in the Astrophysical Journal. High resolution postscript figures can be obtained by anonymous ftp from ftp://ftp.msi.umn.edu/pub/users/twj/sn