Accretion flow dynamics of a few transient black hole candidates from their spectral evolution study using TCAF solution

To understand accretion flow dynamics around black hole candidates (BHCs) one needs to study spectral as well as temporal features in details. After the inclusion of Chakrabarti-Titarchuk two Component Advective Flow (TCAF) model into HEASARC's spectral analysis package XSPEC as a local additive table model, we found that it is quite capable of fitting spectra from different phases of few transient black hole candidates (TBHCs) during their X-ray outbursts. From spectral fits with TCAF model, one can directly extract physical flow parameters, such as two types of accretion (Keplerian disk and sub-Keplerian halo) rates and shock parameters (location and strength of the shock). A much better understanding of spectral and timing properties is achieved by studying evolution of these physical flow parameters during the outbursts of TBHCs. One can also predict frequency of primary dominating QPOs from TCAF fitted shock parameters. Based on a comparison of halo to disk accretion rate ratio (ARR) with quasi-periodic oscillation (QPOs; if present) frequencies, a physical understanding of the classification of the entire outburst phase of the BHCs into different spectral states emerges. We conclude that TCAF in XSPEC, provides us with a better tool to understand accretion flow dynamics during the outbursts of TBHCs.