1. J. W. M. Baars, I. I. K. Pauliny-Toth, and A. Witzel, Astron. Astrophys. 61, 99 (1977).
2. R. F. Carswell and P. A. Strittmatter, Nature 242, 396 (1973).
3. V. A. Efanov, I. G. Moiseev, N. S. Nesterov, et al., Izv. Krym. Astrofiz. Obs. 64, 103 (1981).
4. O. M. Kolkman, The Westerbork Synthesis Radio Telescope User Documentation, Version 1.0.0. (Netherlands Foundation for Research in Astronomy, Dwingeloo, 1993).
5. A. R. Minns and J. M. Riley, Mon. Not. R. Astron. Soc. 315, 839 (2000).