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Astron. Astrophys. 339, 201-207 (1998)

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The expansion of Cassiopeia A as seen in X-rays

Jacco Vink, Hans Bloemen, Jelle S. Kaastra and Johan A.M. Bleeker

SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Received 17 April 1998 / Accepted 3 August 1998


We have for the first time measured the overall expansion rate of the supernova remnant Cas A as seen in X-rays using ROSAT and Einstein HRI images with time differences up to almost 17 years. The overall expansion timescale of Cas A is found to be [FORMULA] yr. This is significantly shorter than the timescale based on high resolution radio data. Although the results clearly indicate that Cas A is not anymore in the free expansion phase, the discrepancy between the radio and X-ray timescales cannot be easily understood. Furthermore, the expansion rate is incompatible with that predicted by a self-similar model for a supernova remnant ploughing through the wind of its progenitor.

Key words: ISM: individual objects: Cas A – ISM: supernova remnants – X-rays: ISM

Send offprint requests to: J.Vink@sron.nl

© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998