Numerical Simulation Of Spectral And Timing Properties Of Galactic Black Holes

TL;DR

This paper uses numerical simulations to analyze the spectral and timing properties of the two-component advective flow model around galactic black holes, incorporating both Keplerian and sub-Keplerian flows for the first time.

Contribution

It presents the first coupled hydrodynamic and Monte Carlo simulation of the TCAF model including both flow components, validating key conjectures about black hole accretion.

Findings

Simulated spectral and timing features match observed black hole data.

First demonstration of combined Keplerian and sub-Keplerian flow simulation.

Validated the role of CENBOL in spectral state transitions.

Abstract

A black hole accretion may have both the Keplerian and the sub-Keplerian components. We consider the most general accretion flow configuration, namely, two-component advective flow (TCAF) in which the Keplerian disk is immersed inside a low angular momentum, accreting sub-Keplerian halo component around a black hole. Low energy (soft) photons from the Keplerian component and hot electrons in the sub-Keplerian component exchange their energy through Comptonization or inverse-Comptonization processes. In the sub-Keplerian component, a shock is generally formed due to the centrifugal force. The post-shock region is known as the CENtrifugal pressure dominated BOundary Layer (CENBOL). The spectral and the timing properties of TCAF have been extensively studied using mostly analytical and some time dependent numerical simulations since the model was proposed by Chakrabarti & Titarchuk in 1995. The findings are the key inputs of understanding several observed features of black hole candidates. In this thesis, using numerical simulation, we rigorously prove some of the conjectures of the TCAF model. In the work presented in this thesis, we have considered for the first time the presence of both the Keplerian and the sub-Keplerian flow in a single simulation. The Keplerian disk resides on the equatorial plane and is the standard disk from which low energy photons having multi-color blackbody spectrum is emitted. The hydrodynamics as well as the thermal properties of the sub-Keplerian halo are simulated using a finite difference code which uses the principle of total variation diminishing (TVD). The Comptonization between the photons and the hot electrons is simulated using a Monte Carlo code. These two codes are then coupled and the resulting localized heating and cooling are included in the coupled code. Using this code, we study the spectral and timing properties of the TCAF.