1. W. Misner, K. Thorne, and J. A. Wheeler,Gravitation(Freeman, San Francisco, 1973), p. 763.
2. H. R. Mille, and P. Witta,Active Galactic Nuclei(Springer, Berlin, 1987) p. 202.
3. Theory of extragalactic radio sources
4. Theory of pulsar magnetospheres