tokens: Acknowledgments We thank Elisa Costantini for helpful discussions and comments. CJ acknowledges valuable discussions with Lynne Valencic about the cosmic abundances. The anonymous referee is appreciated for providing insightful comments and suggestions, which allowed us to improve this paper significantly. We would also like to thank the XMMNewton team for providing important instructions on technical and calibration issues. This project is supported by the Bundesministerium fr Wirtschaft und Technologie/Deutsches Zentrum fr Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OR 1408 and FKZ 50 OR 1604) and the Max Planck Society. This work is based on observations obtained with XMMNewton , an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. The scientific results reported in this paper are also based on observations made by the Chandra X-ray Observatory, as well as data obtained from the Chandra Data Archive. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application packages ciao , chips and sherpa .
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