3 pages, 1 figure, contribution to proceedings of International
  Astrophysics Conference "Relativistic Astrophysics and Cosmology-Einsteins
  Legacy", held during November 7-11, 2005, Munich, Germany. To be printed in
  the Springer-Verlag series "ESO Astrophysics Symposia", Eds. B. Aschenbach,
  V. Burwitz, G. Hasinger, and B. Leibundgut