Chandra Imaging and Spectroscopy of the Eastern XA Region of the Cygnus   Loop Supernova Remnant
  The XA region of the Cygnus Loop is a bright knot of X-ray emission on the eastern edge of the supernova remnant resulting from the interaction of the supernova blast wave with density enhancements at the edge of a precursor formed cavity. To study the nature and origin of the X-ray emission we use high spatial resolution images from Chandra. Our goal is to probe the density of various spectral extraction regions to form a picture of the cavity wall and characterize the interaction between this supernova and the local interstellar medium. We find that a series of regions along the edge of the X-ray emission appears to trace out the location of the cavity wall. The best fit plasma models result in two temperature component equilibrium models for each region. The low temperature components have densities that are an order of magnitude higher than the high temperature components. The high density plasma may exist in the cavity wall where it equilibrates rapidly and cools efficiently. The low density plasma is interior to the enhancement and heated further by a reverse shock from the wall. Calculations of shock velocities and timescales since shock heating are consistent with this interpretation. Furthermore, we find a bright knot of emission indicative of a discrete interaction of the blast wave with a high density cloud in the cavity wall with a size scale ~0.1 pc. Aside from this, other extractions made interior to the X-ray edge are confused by line of sight projection of various components. Some of these regions show evidence of detecting the cavity wall but their location makes the interpretation difficult. In general, the softer plasmas are well fit at temperatures kT~0.11 keV, with harder plasmas at temperatures of kT~0.27 keV. All regions display consistent metal depletions most notably in N, O, and Ne at an average of 0.54, 0.55, and 0.36 times solar. 
Randall L. McEntaffer and Thomas Brantseg
astro-ph.HE