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

Properties of large area ErBa2Cu3O(7-x) thin films deposited by ionized cluster beams

ErBa2Cu3O(7-x) films have been produced by simultaneous deposition of Er, Ba, and Cu from three ionized cluster beam (ICB) sources at acceleration voltages of 0.3 to 0.5 kV. Combining ozone oxidation with ICB deposition at 650 C eliminated any need of post annealing processing. The substrates were rotated at 10 rotations per minute during the deposition which took place at a rate of about 3 to 4 nm. Films with areas up to 70 mm in diameter have been made by ICB deposition. These films, 100 nm thick, were deposited on SrTiO3 (100) substrates at 650 C in a mixture of six percent O3 in O2 at a total pressure of 4 x 10(exp -4) Torr. They had T(sub c) ranging from 84.3 K to 86.8 K over a 70 mm diameter and J(sub c) above 10(exp 6) A/sq cm at 77 K. X ray diffraction measurements of the three samples showed preferential c-axis orientation normal to the substrate surface. Scanning electron micrographs (SEM) of the three samples also show some texture dependence on sample position. For the three samples, there is a correlation between SEM texture, full width at half-maximum of rocking curves and J(sub c) versus temperature curves

Environmental Impact on the Southeast Limb of the Cygnus Loop

We analyze observations from the Chandra X-ray Observatory of the southeast knot of the Cygnus Loop supernova remnant. In this region, the blast wave propagates through an inhomogeneous environment. Extrinsic differences and subsequent multiple projections along the line of sight rather than intrinsic shock variations, such as fluid instabilities, account for the apparent complexity of the images. Interactions between the supernova blast wave and density enhancements of a large interstellar cloud can produce the morphological and spectral characteristics. Most of the X-ray flux arises in such interactions, not in the diffuse interior of the supernova remnant. Additional observations at optical and radio wavelengths support this account of the existing interstellar medium and its role in shaping the Cygnus Loop, and they demonstrate that the southeast knot is not a small cloud that the blast wave has engulfed. These data are consistent with rapid equilibration of electron and ion temperatures behind the shock front, and the current blast wave velocity v_{bw} approx 330 km/s. Most of this area does not show strong evidence for non-equilibrium ionization conditions, which may be a consequence of the high densities of the bright emission regions.Comment: To appear in ApJ, April 1, 200

Live and Learn: Depoliticizing the Interim Appointments of U.S. Attorneys

Following the U.S. Attorney purge of 2006-2007, it is time to reassess the approach used to appoint interim U.S. Attorneys. Recent events have taught us how quickly U.S. Attorneys can become political pawns. Indeed, this scandal has jeopardized the credibility of federal prosecutors, disillusioned career prosecutors in those positions, and called into question the separation between professionalism and politics in the enforcement of our federal laws. To restore confidence in U.S. Attorneys Offices, a reexamination of the interim appointment process is critical so that the mistakes of 2006 are not repeated