Poynting vector in stationary axisymmetric electrovacuum spacetimes   reexamined
  A simple formula, invariant under the duality rotation \Phi -> exp(i\alpha) \Phi, is obtained for the Poynting vector within the framework of the Ernst formalism, and its application to the known exact solutions for a charged massive magnetic dipole is considered. 
V.S. Manko, E.D. Rodchenko, B.I. Sadovnikov and J. Sod-Hoffs