We have performed a comprehensive spectral and timing analyses of Galactic black hole transients ( GBHTs ) during outburst decay in order to obtain the distribution of state transition luminosities .
Using the archival data of the Rossi X-ray Timing Explorer ( RXTE ) , we have calculated the weighted mean for state transition luminosities of 11 BH sources in 19 different outbursts and for disk and power-law luminosities separately .
We also produced histograms of these luminosities in terms of Eddington luminosity fraction ( ELF ) and fitted them with a Gaussian .
Our results show the tightest clustering in bolometric power-law luminosity with a mean logarithmic ELF of -1.70 \pm 0.21 during the index transition ( as the photon index starts to decrease towards the hard state ) .
We obtained mean logarithmic ELF of -1.80 \pm 0.25 during the transition to the hard state ( as the photon index reaches the lowest value ) and -1.50 \pm 0.32 for disk blackbody luminosity ( DBB ) during the transition to the hard-intermediate state ( HIMS ) .
We discussed the reasons for clustering and possible explanations for sources that show a transition luminosity significantly below or above the general trends .