16 research outputs found
Three Dimensional Simulations of Advective, Sub-Keplerian Accretion Flow onto Non-rotating Black Holes
We study the time evolution of sub-Keplerian transonic accretion flow onto a
non-rotating black hole using a three-dimensional, inviscid hydrodynamics
simulation code. Prior two-dimensional simulations show that centrifugal
barrier in the accreting matter may temporarily halt the nearly free-falling
matter and produce a stable, geometrically thick disk which may contain
turbulent eddies. Our goal in this work is to investigate whether the disk
develops any instability because of this turbulence when we dynamically
activate all three dimensions. We find that the disk remains stable and
axisymmetric even close to the central black hole. However, if we explicitly
apply non-axisymmetric azimuthal perturbation, the axisymmetric structure of
the disk is destroyed and instability is developed.Comment: 15 pages, 15 figures, accepted in MNRA
Monte-Carlo Simulations of Thermal Comptonization Process in a Two Component Accretion Flow Around a Black Hole in presence of an Outflow
A black hole accretion may have both the Keplerian and the sub-Keplerian
component. In the so-called Chakrabarti-Titarchuk scenario, the Keplerian
component supplies low energy (soft) photons while the sub-Keplerian component
supplies hot electrons which exchange their energy with the soft photons
through Comptonization or inverse Comptonization processes. In the
sub-Keplerian component, a shock is generally produced due to the centrifugal
force. The postshock region is known as the CENtrifugal pressure-supported
BOundary Layer (CENBOL). In this paper, we compute the effects of the thermal
and the bulk motion Comptonization on the soft photons emitted from a Keplerian
disk by the CENBOL, the preshock sub-Keplerian disk and the outflowing jet. We
study the emerging spectrum when the converging inflow and the diverging
outflow (generated from the CENBOL) are simultaneously present. From the
strength of the shock, we calculate the percentage of matter being carried away
by the outflow and determine how the emerging spectrum depends on the outflow
rate. The preshock sub-Keplerian flow is also found to Comptonize the soft
photons significantly. The interplay between the up-scattering and
down-scattering effects determines the effective shape of the emerging
spectrum. By simulating several cases with various inflow parameters, we
conclude that whether the preshock flow, or the postshock CENBOL or the
emerging jet is dominant in shaping the emerging spectrum depends strongly on
the geometry of the flow and the strength of the shock in the sub-Keplerian
flow.Comment: 15 pages, 8 figure