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tokens: We thank the referee for useful comments that helped to improve the manuscript. We also thank Prof. R. A. Chevalier and Dr D. Caprioli for critically reading the manuscript. MP acknowledges support for this work by NASA through Einstein Post-doctoral Fellowship grant number PF3 140113 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060.