tokens: Acknowledgements The authors thank the referee for their very useful comments. This work has been financially supported by the Programme National Hautes Energies (PNHE), project 994584. LO and AN thank Integrated Activities in the High Energy Astrophysics Domain project for support that enabled this work. L.O. acknowledges support from the DLR grant 50 OR 1612. TB was supported by the FNP grant TEAM/2016-3/19. LO and TB thank Kavli Institute for Theoretical Physics, University of California, where this project have been initiated, for their support. This research has made use of the SIMBAD database, the VizieR catalogue access tool, operated at CDS, Strasbourg, France, and the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. The scientific results reported in this article are based to a significant degree on the data obtained from the Chandra and XMM-Newton Data Archives.
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