1. Swedish Institute of Space Physics, Box 812, S-98 128, Kiruna, Sweden.
2. Centre d'Etude Spatiale des Rayonnements, BP-4346, F-31028 Toulouse, France.
3. Southwest Research Institute, San Antonio, TX 78228–0510, USA.
4. Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamichara, Japan.
5. Mullard Space Science Laboratory, University College London, Surrey RH5 6NT, UK.