1. Backer D.C., Kulkarni S.R., Heiles C., Davis M.M., Goss W.M., 1982, Nat 300, 615
2. Barthel P.D., Schilizzi R.T., Miley G.K., Jägers W.J., Strom R.G., 1985, A&A 148, 243
3. Blandford R.D., Rees M.J., 1974, MNRAS 169, 395
4. Bosma A., 1978, Doctoral thesis, Groningen University
5. Brinks E, Bajaja E., 1986, A&A 169, 14