The X-ray expansion of the supernova remnant Cassiopeia A

Barron Koralesky, L. Rudnick, E. V. Gotthelf, J. W. Keohane

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35 Scopus citations


We present the first X-ray expansion measurements of the young, bright supernova remnant Cas A. We have acquired a deep (232 ks) ROSAT high-resolution image of Cas A that is compared with archival images of similar quality taken 17 yr earlier with the Einstein Observatory. The average expansion rate between the two epochs is found to be 0.20% ± 0.01% yr-1, twice as fast as the expansion of the bright radio ring and two-thirds as fast as the ensemble of optical fast-moving knots. This argues that we are observing a fundamentally different hydrodynamical structure in each band, although all of these components are located on the same patchy ring. In addition, we detect significant variations in the expansion rate as a function of azimuth around the bright X-ray ring. These results are discussed in the context of two classes of models, one involving a preexisting circumstellar shell and the other having a uniform or gradiated density profile that decreases monotonically away from the center.

Original languageEnglish (US)
Pages (from-to)L27-L30
JournalAstrophysical Journal
Issue number1 PART II
StatePublished - 1998

Bibliographical note

Funding Information:
3The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Funding Information:
SNR research at the University of Minnesota is supported by the NASA Graduate Research Program and the National Science Foundation under grant AST 96-19438. We would like to thank T. W. Jones and S. P. Reynolds for discussions about SNR dynamics and comments on the Letter and R. Petre for assistance with the ROSAT observations.


  • ISM: Individual (Cassiopeia A)
  • ISM: Kinematics and dynamics
  • Supernova remnants


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