1. Dolan, J.F., 1972, Astrophys. Space Sci., 17, 472.
2. Lloyd, K.H., 1969, Am. J. Phys., 37, 329.
3. Blisset, R.J. and A.M. Cruise, 1979, MNRAS, 186, 45.
4. Gursky, H. and D. Schwartz, in X-ray Astronomy, R. Giacconni and H. Gursky, eds., 1974, D. Reidel Publishing Company.
5. Brown, R.L. and R.J. Gould, 1970, Phys. Rev., D, 1, 2252.