1. Max-Planck-Institut für Kernphysik, D-69117 Heidelberg, Germany
2. Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA
3. Kirchhoff Institute for Physics, Heidelberg University, D-69120 Heidelberg, Germany
4. Faculty of Physics, Weizmann Institute of Science, Rehovot 76100, Israel