Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555; on observations made with the Chandra X-ray Observatory, operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060; and on observations made with the Canada-France-Hawaii Telescope (CFHT) operated by the National Research Council of Canada, the Institut des Sciences de l'Univers of the Centre National de la Recherche Scientifique and the University of Hawaii.

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Appendices A and B are only available in electronic form at http://www.edpsciences.org

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... Astronomie

Founded by merging of the Institut für Astrophysik und Extraterrestrische Forschung, the Sternwarte, and the Radioastronomisches Institut der Universität Bonn.

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... CIAO v3.1 package

Chandra Interactive Analysis of Observations (CIAO), http://cxc.harvard.edu/ciao/

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... page

http://www.astro.psu.edu/xray/acis/recipes/clean.html

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