1. Abrosimov, A. T., Gvozdev, I. K., Illarionova, N. V., Kovrizhnykh, O. M., Kudryavtsev, M. I., Logachev, Yu. I., and Petrov, V. M.: 1988, Solar Hard X-ray Bursts on Prognoz-9, Materials of World Data Center-B, Moscow.
2. Akin'jan, S. T.: 1973, Astron. Zh. 50, 806 (in Russian).
3. Belovsky, M. N. and Ochelkov, Yu. P.: 1979, Doklady ANSSSR 236, 13316 (in Russian).
4. Bogovalov, S. V., Kotov, Yu. D., and Zenchenko, V. M.: 1985, Pis'ma v Astron. Zh. 11, 763 (in Russian).
5. B�hme, A., F�rstenberg, F., Hildebrandt, J., Kr�ger, A., Hoyong, P., and Stevens, G. A.: 1976, HHI-STP Report No. 6, Berlin.