1. Aharonian, F. A., Kirillov-Ugrumov, V. G., and Vardanian, V. V.: 1985,Astrophys. Space Sci. 115, 201.
2. Berezinsky, V. S.: 1986, in V. L. Ginzburg (ed.),Cosmic Ray Astrophysics, Ch. 7, Nauka, Moscow (in Russian).
3. Burns, M. L. and Lovelace, R. V. E.: 1982,Astrophys. J. 262, 87.
4. Honda, M.: 1989,Astrophys. J. 339, 629.
5. Ivanenko, I. P. and Sizov, V. V.: 1987,Proc. 20th Int. Cosmic Ray Conf., Moscow 5, 391.