X-ray Emission from Strongly Asymmetric Circumstellar Material in the
  Remnant of Kepler's Supernova
  Kepler's supernova remnant resulted from a thermonuclear explosion, but is
interacting with circumstellar material (CSM) lost from the progenitor system.
We describe a statistical technique for isolating X-ray emission due to CSM
from that due to shocked ejecta. Shocked CSM coincides well in position with 24
$\mu$m emission seen by {\sl Spitzer}. We find most CSM to be distributed along
the bright north rim, but substantial concentrations are also found projected
against the center of the remnant, roughly along a diameter with position angle
$\sim 100^\circ$. We interpret this as evidence for a disk distribution of CSM
before the SN, with the line of sight to the observer roughly in the disk
plane. We present 2-D hydrodynamic simulations of this scenario, in qualitative
agreement with the observed CSM morphology. Our observations require Kepler to
have originated in a close binary system with an AGB star companion.
