1. Physics Department, University of Crete, GR 71003, Heraklion, Greece
2. Institute of Astrophysics, Foundation for Research and Technology – Hellas, GR 71110 Heraklion, Greece
3. Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4. Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman Avenue, Evanston, IL 60201, USA
5. NASA Goddard Space Flight Center, Laboratory for X-ray Astrophysics, Greenbelt, MD 20771, USA
6. Department of Physics, University of Maryland Baltimore County, Baltimore, MD 21250, USA
7. Geneva Observatory, University of Geneva, Chemin des Maillettes 51, CH-1290 Sauverny, Switzerland
8. Department of Physics and Astronomy, The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218, USA
9. Department of Physics, University of Arkansas, 825 West Dickson Street, Fayetteville, AR 72701, USA