1. Bialk, M., Dr�ge, W., and Heber, B.: 1991, Proc. 22nd Int. Cosmic Ray Conf. 3, 764.
2. Cane, H. V. and Reames, D. V.: 1990, Astrophys. J. Suppl. 73, 253.
3. Cane, H. V., McGuire, R. E., and von Rosenvinge, T. T.: 1986, Astrophys. J. 301, 448.
4. Cliver, E. W. and Kahler, S. W.: 1991, Astrophys. J. 366, L91.
5. Dulk, G. A., Steinberg, J. L., Lecacheux, A., Hoang, S., and MacDowell, R. J.: 1985, Astron. Astrophys. 150, L28.