tokens: Acknowledgements We thank the anonymous referee for the useful comments that improved the manuscript. L.D. thanks Jun Yang for answering some questions about the library of X-ray pulsars in SMC. This paper is based on data from observationswith, XMM-Newton , Swift , and Chandra X-ray observatory. XMM-Newton is an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Chandra data were obtained from the Chandra Data Archive. This paper is based on data from observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Spain, and Switzerland), Czech Republic, and Poland, and with the participation of Russia and the USA. This work is supported by the Bundesministerium für Wirtschaft und Technologie through the Deutsches Zentrum für Luft und Raumfahrt (grant FKZ 50 OG 1602). P.R. acknowledges contract ASI-INAF I/004/11/0.
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