Using the new disk models mentioned above, Shafee et al. (2006) fitted ASCA and RXTE spectral data on the BHB GRO J1655–40 and found . For 4U 1543–47, they found , although this result is based only on RXTE data. The authors consider it unlikely that either BH has a spin close to the theoretical maximum, . On the other hand, in the case of 4U 1543–47, the estimated spin appears too high to be explained by spin up due to accretion, which suggests that their measurements are sensitive to the BH’s natal spin.
Source: Remillard & McClintock 2006 ┃ X-Ray Properties… ⚬𓂃
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