Effects of Compton Cooling on the Hydrodynamic and the Spectral Properties of a Two Component Accretion Flow around a Black Hole

TL;DR

This study uses coupled hydrodynamic and radiative transfer simulations to explore how Compton cooling affects the structure and spectral states of a two-component accretion flow around a black hole, revealing state transitions and spectral features.

Contribution

It introduces a time-dependent simulation coupling hydrodynamics with radiative transfer to analyze accretion flow dynamics and spectral properties around black holes, highlighting the effects of Compton cooling.

Findings

Flow symmetry is broken by soft photon source, becoming axisymmetric.

Centrifugal barrier forms, affecting the spectrum.

State transitions depend on accretion rates.

Abstract

We carry out a time dependent numerical simulation where both the hydrodynamics and the radiative transfer are coupled together. We consider a two-component accretion flow in which the Keplerian disk is immersed inside an accreting low angular momentum flow (halo) around a black hole. The injected soft photons from the Keplerian disk are reprocessed by the electrons in the halo. We show that in presence of an axisymmetric soft-photon source, the spherically symmetric Bondi flow losses its symmetry and becomes axisymmetric. The low angular momentum flow was observed to slow down close to the axis and formed a centrifugal barrier which added new features into the spectrum. Using the Monte Carlo method, we generated the radiated spectra as functions of the accretion rates. We find that the transitions from a hard state to a soft state is determined by the mass accretion rates of the disk and the halo. We separate out the signature of the bulk motion Comptonization and discuss its significance. We study how the net spectrum is contributed by photons suffering different number of scatterings and spending different amounts of time inside the Compton cloud. We study the directional dependence of the emitted spectrum as well.