Effects of Compton cooling on the hydrodynamic and the spectral properties of a two-component accretion flow around a black hole

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 disc is immersed inside an accreting low angular momentum flow (halo) around a black hole. The injected soft photons from the Keplerian disc are reprocessed by the electrons in the halo. We show that in presence of an axisymmetric soft‐photon source the spherically symmetric Bondi flow loses 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 disc 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.

Temporal Variability From the Two-Component Advective Flow Solution and Its Observational Evidence

“…This is precisely what happens in Figure 7. Ghosh et al (2011) found that the same outgoing photons from Monte-Carlo simulations, when binned with respect to inclination angles, showed distinctly harder spectra at higher inclinations.…”

“…On the other hand, Heil et al (2015) found that the amplitude of the broadband noise (subtracting the low-frequency QPOs) is no longer dependent on inclination, implying its correlation with the source structure of the emitting regions. Using Monte-Carlo simulations, Ghosh et al (2011) also find for the same disk flow properties that the spectrum changes with inclination angle.…”

A jet model for Galactic black-hole X-ray sources: The correlation between cutoff energy and phase lag

“…The Comptonizing medium could be an optically thin, very hot corona in the vicinity of the compact object (Sunyaev & Titarchuk 1980;Hua & Titarchuk 1995;Zdziarski 1998), an advection-dominated accretion flow (Narayan & Yi 1994;Esin et al 1997), a low angular momentum accretion flow (Ghosh et al 2011;Garain et al 2012), or the base of a radio jet (Band & Grindlay 1986;Georganopoulos et al 2002). In addition to these components, a discrete line at 6.4 keV is generally observed and attributed to reflection of the hard X-rays from the accretion disk (Fabian et al 1989).…”

Discovery of Jet-Induced Soft Lags of XTE J1550-564 during Its 1998 Outburst †

“…On the other hand, lags are associated with fluctuation of thermodynamical parameters like density, temperature, reflection coefficient of the Keplerian disk and interception fraction of the soft photons (see [18] for further details). Recent studies of spectral (see [31], [32] and [33] for further details) and temporal (see [1]) variabilities showed significant spectral hardening and QPO ν c and/or rms variation due to inclination angle variation. Later, similar inclination dependency of lag signs were seen (see [9] and [10]).…”