The Evolution of Cassiopeia A as a Function of Azimuth

by Barron Thomas Koralesky

Under the supervision of Professor Lawrence Rudnick


We measured the dynamics of Cas A in the radio over 11 years. Cas A is seen to be in a variety of evolutionary states and the Sedov exponent is found to vary from 0.2-0.5 at different azimuths. The variations have a characteristic scale of 45-60° of azimuth. If the bright ring illuminates the inner shock or contact discontinuity, then the expansion factors indicate CasA is in a pre-Sedov state; a Sedov state is not likely. Large azimuthal asymmetries in Cas A are seen in spectral index and change in brightness over 11 years. The change in brightness is correlated with the expansion factor. This correlation shows that the faster moving areas are losing the least flux. This suggests re-acceleration of particles or magnetic field amplification. These areas have a decrease in fractional polarization, indicating that the dominant amplification method is destroying order in the magnetic field.