Kerr Parameters for Stellar Mass Black Holes and Their Consequences for   GRBs and Hypernovae
  Recent measurements of the Kerr parameters a* for two black-hole binaries in our Galaxy (Shafee et al. 2006), GRO J1655-40 and 4U 1543-47 of a*=0.65-0.75 and a*=0.75-0.85, respectively, fitted well the predictions of Lee et al. (2002), of a*= 0.8. In this report we also note that Lee et al. (2002) predicted a* >0.5 for 80% of the Soft X-ray Transient Sources. The maximum available energy in the Blandford-Znajek formalism for a* > 0.5 gives E > 3 x 10^{53} ergs, orders of magnitude larger than the energy needed for the GRB and hypernova explosion. We interpret the Soft X-ray Transients to be relics of GRBs and Hypernovae, but most of them were subluminous ones which could use only a small part of the available rotational energy. 
E. Moreno Mendez, G.E. Brown, C.-H. Lee, F.M. Walter