Is Compton cooling sufficient to explain evolution of observed quasi-periodic oscillations in Outburst sources?

TL;DR

This study demonstrates that inverse Compton cooling alone can sufficiently explain the evolution of QPO frequencies in black hole outburst sources within the TCAF model, supported by observational data from H1743-322.

Contribution

It shows that Compton cooling can account for QPO evolution without additional mechanisms, using detailed modeling of the Compton cloud's dynamics during outburst.

Findings

Cooling of the Compton cloud explains QPO frequency increase during rising phase.

Estimated viscosity parameter $mbda$ rises monotonically from 0.0001 to 0.02.

Inward velocity of the Compton cloud is a few meters per second.

Abstract

In outburst sources, quasi-periodic oscillation (QPO) frequency is known to evolve in a certain way: in the rising phase, it monotonically goes up till a soft intermediate state is achieved. In the propagating oscillatory shock model, oscillation of the Compton cloud is thought to cause QPOs. Thus, in order to increase QPO frequency, Compton cloud must collapse steadily in the rising phase. In decline phases, exactly opposite should be true. We investigate cause of this evolution of the Compton cloud. The same viscosity parameter which increases the Keplerian disk rate, also moves the inner edge of the Keplerian component, thereby reducing the size of the Compton cloud and reducing the cooling time scale. We show that cooling of the Compton cloud by inverse Comptonization is enough for it to collapse sufficiently so as to explain the QPO evolution. In the Two Component Advective Flow (TCAF) configuration of Chakrabarti-Titarchuk, centrifugal force induced shock represents boundary of the Compton cloud. We take the rising phase of 2010 outburst of Galactic black hole candidate H~1743-322 and find an estimation of variation of $\alpha$ parameter of the sub-Keplerian flow to be monotonically rising from $0.0001$ to $0.02$, well within the range suggested by magneto-rotational instability. We also estimate the inward velocity of the Compton cloud to be a few meters/second which is comparable to what is found in several earlier studies of our group by empirically fitting the shock locations with the time of observations.