1. Berry, E. V., Hess, V.: 1942, Terr. Mag. 47, 251.
2. Chupp, E. L., Forrest, D. J., Higbie, P. R., Suri, A. N., Tsai, C., Dunphy, P. P.: 1973, Nature 241, 333.
3. Chupp, E. L.: 1981, in R. E. Lingenfelter, H. S. Hudson and D. M. Worrall (eds.), Gamma Ray Transients and Related Astrophysics, Amer. Inst. of Physics, New York, p. 363.
4. Chupp, E. L., Forrest, D. J., Ryan, J. M., Heslin, J., Reppin, C., Pinkau, K., Kanbach, G., Rieger, E., Share, G. H.: Astrophys. J. (Letters) 236, L95.
5. DeBrunner, H., Flueckiger, E., Golliez, F., Neuenschwander, H., Schubnell, M., Sebor, G.: 1982, Physikalisches Institute, University of Bern, Switzerland, Private Communication.