Part of this work was performed under EC-twinning contract No. SCI*-CT91-0727 on Coherent Radiation and Particle Acceleration in Magnetized Plasmas, and CEC HCM Network ERBCHRXCT 940604 on Energetic Particles in Astrophysical and Space Plasmas. M.A.-S. and G.R. gratefully acknowledge postdoctoral institutional fellowships from the EC on Astrophysics of Accretion and Winds near Compact Objects under contract number ERBCHBGCT 93-0998. D.S. gratefully acknowledges support from the Erasmus programm ICP-94-B-3047/13 for a visit to St. Andrews. It is a pleasure to thank Bram Achterberg, Bob Bingham, Yves Gallant and Michel Tagger for their comments.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998