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We study several Galactic black hole candidates using long-time RXTE/ASMX-ray data to search for telltale signatures of differences in viscoustimescales in the two components used in the Two-Component Advective Flow(TCAF) paradigm. In high-mass X-ray binaries (HMXBs) mainly winds are accreted.This nearly inviscid and dominant sub-Keplerian flow falls almost freelytowards the black hole. A standard Keplerian disc can form out of thissub-Keplerian matter in presence of a significant viscosity and could be smallin size. However, in low-mass X-ray binaries (LMXBs), highly viscous and largerKeplerian accretion disc is expected to form inside the sub-Keplerian disc dueto the Roche-lobe overflow. Due to two viscous timescales in these twocomponents, it is expected to have a larger lag between the times-of-arrival ofthese components in LMXBs than that in HMXBs. Direct cross-correlation betweenthe photon fluxes will not reveal this lag/delay since they lack lineardependence; however, they are coupled through the viscous processes which bringin both matter. To quantify the aforesaid time lag, we introduce an index({\Theta}), which is a proxy of the usual photon index ({\Gamma}). Thus, when{\Theta}, being dynamically responsive to both fluxes, is considered as areference, the arrival time lag between the two fluxes in LMXBs is found to bemuch larger than that in HMXBs. Our result establishes the presence of twodynamical components in accretion and shows that the Keplerian disc size indeedis smaller in HMXBs as compared to that in LMXBs.

Signature of Two-Component Advective Flow in several Black Hole candidates obtained through time-of-arrival analysis of RXTE/ASM Data