A Multiwavelength Study of Cassiopeia A and Kepler's Supernova Remnants
by Tracey Ann DeLaney
Under the supervision of Professor Larry Rudnick
A multiwavelength comparison of X-ray, infrared, optical, and radio images for Cassiopeia A (Cas A) and Kepler's supernova remnants has been conducted to construct a coherent physical picture of the multiple interacting thermal and relativistic plasmas. In addition, high-resolution X-ray proper motions of compact features in Cas A have been measured over a two-year baseline.
The X-ray emission in Cas A can be separated into four spectrally and kinematically distinct classes that have clear associations to the emission in the other three wavebands. The emitting material is classified into two components -- shocked circumstellar medium (CSM) and shocked ejecta, which show the same respective morphologies and proper motions in the different bands. In the shocked CSM, we find matched low-energy enhanced X-ray emission and optical quasi-stationary flocculi, and X-ray continuum-dominated emission matched with filamentary radio structures. We also find hybrid X-ray low-energy-enhanced/continuum-dominated emission matched to 24 μm dust emission in the CSM. In the shocked ejecta, we find matched silicon and iron dominated X-ray emission and optical fast-moving knots. Based on the kinematic and morphological results, we propose evolutionary scenarios for the ejecta and circumstellar material in Cas A.
In Kepler's supernova remnant, we also find clear associations between the emission in the four wavebands. The ejecta are defined by matching steep-spectrum radio emission and X-ray emission. The forward shock is identified by a ring of continuum-dominated X-ray emission, flat-spectrum radio emission, and filamentary optical Balmer-dominated emission. The clumpy circumstellar medium is identified by knotty optical emission, mid-infrared dust emission, and some matching X-ray emission. To the south the forward and reverse shocks have separated, whereas to the north there is little separation. There is an anti-correlation between the flat-spectrum radio synchrotron emission and the thermal emission to the north suggesting a relative weakening of the particle acceleration at the forward shock due to Alven wave damping.