We tabulate the luminosities of the soft-to-hard state transitions of all X-ray binaries for which there exist good X-ray flux measurements at the time of the transition , good distance estimates , and good mass estimates for the compact star .
We show that the state transition luminosities are at about 1-4 % of the Eddington rate , markedly smaller than those typically quoted in the literature , with a mean value of 2 % .
Only the black hole candidate GRO J 1655-40 and the neutron star systems Aql X-1 and 4U 1728-34 have measured state transition luminosities inconsistent with this value at the 1 \sigma 
level .
GRO J 1655-40 , in particular , shows a state transition luminosity below the mean value for the other sources at the 4 \sigma 
level .
This result , combined with the known inner disk inclination angle ( the disk is nearly parallel to the line of sight ) from GRO J 1655-40 ’ s relativistic jets suggest that the hard X-ray emitting region in GRO J 1655-40 can have a velocity of no more than about \beta = 0.68 , with a most likely value of about \beta = 0.52 , and a minimum speed of \beta = 0.45 , assuming that the variations in state transition luminosities are solely due to relativistic beaming effects .
The variance in the state transition luminosities suggests an emission region with a velocity of \sim 0.2 c .
The results are discussed in terms of different emission models for the low/hard state .
We also discuss the implications for measuring the dimensionless viscosity parameter \alpha .
We also find that if its state transitions occur at typical luminosities , then GX 339-4 is likely to be at a distance of at least 7.6 kpc , much further than typically quoted estimates .