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T. J. Gaetz, M. Sasaki (Smithsonian Astrophysical Observatory), W. P. Blair (Johns Hopkins University), R. J. Edgar, P. P. Plucinsky, J. C. Raymond (Smithsonian Astrophysical Observatory), R. K. Smith (NASA/Goddard), A. H. Szentgyorgyi (Smithsonian Astrophysical Observatory)
Understanding the interaction of supernova remnants with inhomogeneities in the surrounding medium is important for unraveling the dynamics and evolution of the interstellar medium. The Cygnus Loop supernova remnant is a cavity remnant in which the blast wave has recently encountered the walls of the cavity. The ``XA'' region lies in an indentation on the eastern rim resulting from the blast wave encountering a large cloud; the bright triangle of optical emission has been interpreted as the interaction of a shock with a long finger of material protruding into the cavity. In X-rays, this region is particularly bright and soft. We have imaged it with Chandra using the ACIS-S3 aimpoint. The X-ray emission is very soft, predominantly H-like and He-like lines of Oxygen; toward the east it is dominated by even softer emission. This makes the analysis sensitive to the low-energy calibration. We present spatial and spectral analyses incorporating recent improvements in understanding the low energy ACIS response. We combine X-ray and optical data to examine the optical XA feature; the optical data show complex structure, and the Chandra data also show complex spatial and spectral structure with both correlations and anti-correlations with optical features. Along the north side of the interaction, H\alpha and [O III] emission are brighter, with indications of Kelvin-Helmholtz instabilities. The Chandra data show diffuse emission in the north, and a bright knotty ridge of emission along the southern face; this ridge appears to be related to a shock marked by a filaments seen in H\alpha, [O III], and [Ne V]. The combination of X-ray data and optical/UV data provide further insight on the shock/cloud interaction problem.
This work was supported by NASA grants G01-2060X and NAG5-9978, and by NASA contract NAS8-03060.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.