arXiv subjects

Sudip K Garain

Publications and source records attributed to Sudip K Garain.

6 recordsLinked to original sources

arXiv2026

Simulation based parameter space for shock in transonic, sub-Keplerian accretion flow onto non-rotating black holes

Non-dissipative, transonic, sub-Keplerian accretion flow onto black holes is characterized by two conserved parameters: specific energy and specific angular momentum of the flow. For certain range of these parameters, the accretion flow shows shock formation and the post-shock matter forms a boundary layer which is believed to shape the radiative properties of the accretion disk. In this work, we identify the parameter space for shock in such accretion flows using multi-dimensional numerical simulations around non-rotating black holes and demonstrate that the shock formation parameter space is much larger than the analytically calculated one. We also find the boundary layer to be dynamic for a significant part of this parameter space and self-consistently produce outflow from the accretion disk.

astro-ph.HE↗

arXiv2026

Outflow from unmagnetized shocked radiative transonic accretion disk around a black hole

We study outflow from an unmagnetized, shocked accretion disk around a non-rotating super-massive black hole using multidimensional hydrodynamics simulation with radiative cooling. We aim to investigate whether such shocked accretion flow can launch sustained collimated bipolar outflow reaching out to thousands of gravitational radii even in the absence of magnetic field and if yes, what terminal velocity can they achieve? We present the results of a few simulations of geometrically thick accretion flow with increasing specific angular momentum on a vertically elongated cylindrical domain. We show thatbipolar outflow from a region very close to the black hole is originating and propagating vertically out to our simulation domain boundary at around $2651$ Schwarzschild radius. The outflow attains a terminal velocity with a maximum value found to be $0.14c$ and the outflow rate depends on the angular momentum value of the accreting material. We also compute the self-Comptonized bremsstrahlung spectra for all the disk-jet runs.

astro-ph.HE↗

arXiv2025

A general relativistic hydrodynamic simulation code for studying advective, sub-Keplerian accretion flow onto black holes

In this paper, we describe a general relativistic hydrodynamics simulation code which is developed to simulate advective accretion flow onto black holes. We are particularly interested in the accretion simulations of sub-Keplerian matter in the close vicinity of black holes. Due to the presence of centrifugal barrier, a nearly free-falling sub-Keplerian accretion flow slows down close to a black hole and can even pass through shocks before accelerating again to the black hole. We design our simulation code using the high resolution shock capturing scheme so that such shock structures can be captured and analyzed for relevance. In this paper, we describe our implementation and validation of the code against a few known analytical and numerical results of sub-Keplerian matter accretion.

astro-ph.IM↗

arXiv2024

General Relativistic Hydrodynamic Simulations around Accreting Black Holes

Strong gravity in the immediate vicinity of compact objects (e.g., black holes, neutron stars) necessitates inclusion of general relativistic effects. Traditionally, pseudo-Newtonian potential representation of gravity were favored to simulate the fluid motion in this region since that reduced the calculation complexity. However, with the advent of easily implementable, reliable numerical algorithms and computer hardware, more and more research groups are shifting towards the numerical solutions of general relativistic fluid dynamics equations. In this work, we report our progress on the development of such simulation tool and present results of sub-Keplerian accretion flow onto black holes.

astro-ph.HE↗

arXiv2022

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.

astro-ph.HE↗

arXiv2013

Numerical Simulation of Spectral and Timing Properties of a Two Component Advective Flow around a Black Hole

We study the spectral and timing properties of a two component advective flow (TCAF) around a black hole by numerical simulation. Several cases have been simulated by varying the Keplerian disk rate and the resulting spectra and lightcurves have been produced for all the cases. The dependence of the spectral states and quasi-periodic oscillation (QPO) frequencies on the flow parameters is discussed. We also find the earlier explanation of arising of QPOs as the resonance between infall time scale and cooling time scale remain valid even for Compton cooling.

astro-ph.HE↗