1. Achterberg, A. 1981. Astr.Astrophys., 98, 161.
2. Arons, J. 1981. In IAU Symp. No. 94, The Origin of Cosmic Rays, ed. G. Setti, G. Spada and A.W. Wolfendale (Reidel: Dordrecht), p. 175.
3. Arons, J., Max, C. and McKee, C. 1979. (Eds.) Particle Acceleration Mechanisms in Astrophysics (American Institute of Physics: New York).
4. Axford, W.I. 1981. In IAU Symp. No. 94, The Origin of Cosmic Rays, ed. G. Setti, G. Spada and A.W. Wolfendale (Reidel: Dordrecht), p. 339.
5. Axford, W.I. 1982. Preprint.