Constraints on mass ejection in black hole formation derived from black hole X-ray binaries

Both the recently observed high runaway velocities of Cyg X-l (similar to 5 0 km s(-1)) and X-ray Nova Sco 1994 (greater than or equal to 100 km s(-1)) and the relatively low radial velocities of the black hole X-ray binaries with low mass donor stars, can be explained by symmetric mass ejection in t he supernovae (SNe) which formed the black holes in these systems. Assuming symmetric mass ejection in black hole formation, we estimate the a mount of mass that must have been ejected in the stellar core collapse in o rder to explain the velocities of the above X-ray binaries. We find that at least 2.6 M. and 4.1 M. must have been ejected in the formation of Cyg X-l and Nova Sco, respectively. A similar mass loss fraction(f = 0.35) for the black hole binaries with low mass donors, gives low velocities, in agreeme nt with the observations. We conclude that the black holes in X-ray binaries are all consistent with being formed in a successful SN in which mass is ejected. A possible kick a t the formation of the black hole is not needed to explain their space velo cities.