A new epoch of VLA measurements of Kepler ’ s supernova remnant was obtained to make accurate measurements of the radio spectral index variations and polarization .
We have compared these new radio images with H \alpha , infrared , and X-ray data to better understand the three dimensional structure and dynamics of Kepler , and to better understand the physical relationships between the various nonthermal and thermal plasmas .
Spatial variations in the radio spectral index from - 0.85 to - 0.6 are observed between 6 cm and 20 cm .
The mean spectral index is - 0.71 .
The mean percent polarization is 3.5 % at 20 cm and 6 % at 6 cm .
There is a strong correspondence between the radial and azimuthal profiles of the radio , X-ray , H \alpha , and infrared emission in different locations around the remnant although there is no single , global pattern .
Spectral tomography shows that the flat- and steep-spectrum radio emissions have distinct structures .
The flat-spectrum radio emission is found either at a larger radius than or coincident with the steep-spectrum emission .
We interpret these spectral components as tracing forward- and reverse-shocked material , respectively .
The flat-spectrum radio emission can alternatively be interpreted as the bow-shocked material ( reshocked by the forward shock ) from the progenitor ’ s motion through the interstellar medium .
The H \alpha and IR images are very similar .
Their leading edges are coincident and are either in front of or coincident with the leading edges of the X-ray and radio emission .
The X-ray emission matches the H \alpha and IR emission in places , and in other places traces the steep-spectrum radio emission .
In the north there is also an anticorrelation in the azimuthal profiles around the remnant of the flat-spectrum radio emission and the thermal X-ray , H \alpha , and IR emissions .
We suggest that this could be due to a relative weakening of the particle acceleration at the forward shock due to Alfvén wave damping in regions of high density .