D. Horns (1), A.I.D. Hoffmann (1), A. Santangelo (1), F.A. Aharonian
  (2), G.P. Rowell (3) ((1) Institute for Astronomy and Astrophysics,
  University of T\"ubingen, Germany (2) Max-Planck-Institute for Nuclear
  Physics, Heidelberg, Germany (3) School of Chemistry and Physics, University
  of Adelaide, Australia)