Carroll B.W., E.G. Zweibel, C.J. Hansen, P.N. McDermott, M.P. Savedoff, J.H. Thomas, and H.M. Van Horn, The Astrophysical Journal 305, 767 (1986).
McDermott P.N., M.P. Savedoff, H.M. Van Horn, E.G. Zweibel, and C.J. Hansen, The Astrophysical Journal 281, 746 (1984).