scholarly journals Study of Accretion Flow Dynamics of V404 Cygni during Its 2015 Outburst

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 39
Author(s):  
Arghajit Jana ◽  
Jie-Rou Shang ◽  
Dipak Debnath ◽  
Sandip K. Chakrabarti ◽  
Debjit Chatterjee ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Flow Dynamics ◽  
Advective Flow ◽  
Rapid Variation ◽  
Accretion Flow ◽  
Flow Parameters ◽  
Accretion Rates ◽  
Post Shock ◽  
Timing Properties ◽  
Shock Oscillation

The 2015 Outburst of V404 Cygni is an unusual one with several X-ray and radio flares and rapid variation in the spectral and timing properties. The outburst occurred after 26 years of inactivity of the black hole. We study the accretion flow properties of the source during its initial phase of the outburst using Swift/XRT and Swift/BAT data in the energy range of 0.5–150 keV. We have done spectral analysis with the two component advective flow (TCAF) model fits file. Several flow parameters such as two types of accretion rates (Keplerian disk and sub-Keplerian halo), shock parameters (location and compression ratio) are extracted to understand the accretion flow dynamics. We calculated equipartition magnetic field Beq for the outburst and found that the highest Beq∼900 Gauss. Power density spectra (PDS) showed no break, which indicates no or very less contribution of the Keplerian disk component, which is also seen from the result of the spectral analysis. No signature of prominent quasi-periodic oscillations (QPOs) is observed in the PDS. This is due to the non-satisfaction of the condition for the resonance shock oscillation as we observed mismatch between the cooling timescale and infall timescale of the post-shock matter.

scholarly journals Inference on accretion flow properties of XTE J1752-223 during its 2009-10 outburst

2020 ◽  
Vol 493 (2) ◽  
pp. 2452-2462 ◽  
Author(s):  
Kaushik Chatterjee ◽  
Dipak Debnath ◽  
Debjit Chatterjee ◽  
Arghajit Jana ◽  
Sandip K Chakrabarti
Keyword(s):  
Black Hole ◽  
Spectral Analysis ◽  
Low Frequency ◽  
Power Law Model ◽  
Flow Properties ◽  
Advective Flow ◽  
Black Hole Candidate ◽  
Two Component ◽  
Timing Properties ◽  
Spectral States

ABSTRACT Spectral and timing properties of the stellar-mass black hole candidate XTE J1752-223 during its 2009-10 outburst are studied using RXTE PCA data in the 2.5–25 keV energy range. Low frequency quasi-periodic oscillations are seen during outburst. The spectral analysis is done using two types of models: one is the combined disc blackbody plus power-law model and the other is Transonic flow solution based Two Component Advective Flow (TCAF) model. Light-curve profiles and evolution of hardness ratios are studied using MAXI GSC and Swift BAT data. Based on the evolution of the temporal and the spectral properties, we find that the object evolved through the following spectral states: hard, hard-intermediate, and soft-intermediate/soft. From the TCAF model fitted spectral analysis, we also estimate the probable mass of the black hole in the range of 8.1−11.9 M⊙, and more precisely, the mass appears to be 10 ± 1.9 M⊙.

scholarly journals Radiative efficiency of hot accretion flow and the radio/X-ray correlation in X-ray binaries

2014 ◽  
Vol 10 (S312) ◽  
pp. 139-140
Author(s):  
Fu-Guo Xie
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
X Ray ◽  
Radiative Efficiency ◽  
Accretion Flow ◽  
Accretion Rates ◽  
Distinctive Property ◽  
X Ray Binaries

AbstractSignificant progresses have been made since the discovery of hot accretion flow, a theory successfully applied to the low-luminosity active galactic nuclei (LLAGNs) and black hole (BH) X-ray binaries (BHBs) in their hard states. Motivated by these updates, we re-investigate the radiative efficiency of hot accretion flow. We find that, the brightest regime of hot accretion flow shows a distinctive property, i.e. it has a constant efficiency independent of accretion rates, similar to the standard thin disk. For less bright regime, the efficiency has a steep positive correlation with the accretion rate, while for faint regime typical of advection-dominated accretion flow, the correlation is shadower. This result can naturally explain the observed two distinctive correlations between radio and X-ray luminosities in black hole X-ray binaries. The key difference in systems with distinctive correlations could be the viscous parameter, which determines the critical luminosity of different accretion modes.

scholarly journals ACCRETION FLOW DYNAMICS OF MAXI J1659-152 FROM THE SPECTRAL EVOLUTION STUDY OF ITS 2010 OUTBURST USING THE TCAF SOLUTION

2015 ◽  
Vol 803 (2) ◽  
pp. 59 ◽  
Author(s):  
Dipak Debnath ◽  
Aslam Ali Molla ◽  
Sandip K. Chakrabarti ◽  
Santanu Mondal
Keyword(s):  
Flow Dynamics ◽  
Spectral Evolution ◽  
Accretion Flow ◽  
Evolution Study

Shock-induced vorticity variation model of supersonic planar mixing layers

2020 ◽  
pp. 2150059
Author(s):  
Junhong Feng ◽  
Junyong Lu ◽  
Chibing Shen
Keyword(s):  
Mixing Layer ◽  
Numerical Results ◽  
Oblique Shock Wave ◽  
Practical Applications ◽  
Mixing Performance ◽  
Qualitative And Quantitative ◽  
Discontinuous Flow ◽  
Flow Parameters ◽  
Post Shock ◽  
Shock Impingement

Vorticity variation in a supersonic planar mixing layer interacting with an oblique shock wave is investigated analytically and numerically. A model that simplifies the mixing layer to a discontinuous flow is established to solve the post-shock flow parameters, and it is validated through qualitative and quantitative comparisons with the Buttsworth’s model and numerical results. A model to estimate the shock-induced Maximum Vorticity Amplification (MVA) is obtained, which agrees well with the numerical results. The model could estimate the growth rate and maximum vorticity of the shocked mixing layer. The vorticity of the mixing layer is amplified by the shock impingement, even though the vorticity thickness decreases, which can improve the mixing performance for different practical applications.

X-RAY SPECTRAL ANALYSIS OF SU UMa TYPE DWARF NOVAE OBSERVED WITH ROSAT

2003 ◽  
Vol 12 (04) ◽  
pp. 739-755 ◽  
Author(s):  
GÜLNUR ÝKİS GÜN ◽  
E. NİHAL ERCAN
Keyword(s):  
Spectral Analysis ◽  
Quiescent State ◽  
X Rays ◽  
Dwarf Novae ◽  
Spectral Parameters ◽  
X Ray ◽  
Spectral Models ◽  
Accretion Rates ◽  
Mass Evaporation ◽  
Best Fit

X-ray spectral parameters were determined for eight SU UMa type Dwarf Novae observed with the ROSAT PSPC. The raw data were fitted with various spectral models and the best fit spectral models are found to be that of Raymond–Smith and Thermal Bremsstrahlung. The best fit temperatures were estimated to be between kT ~ 1.1-1.8 keV while the Column Densities were found to be between NH ~ 2.4×1020-4.1×1020 cm -2. The estimated 0.1-2.4 keV fluxes were in the range of log FX=-13 to -11 ergs cm-2 s-1. FX/F UV and FX/F opt rates were calculated to be between ~0.09 and ~0.37. This shows that most of the energy is radiated in the Optical and Ultraviolet band from the accretion disk in the quiescent state. Many of the SU UMa type Dwarf Novae show an Ultraviolet lag in their outburst spectrum, the Coronal Siphon Flow Model of Meyer and Meyer-Hofmeister may explain this phenomenon. This model proposes a corona at the boundary layer of a system when it is a quiescent state and suggests that some parts of the X-rays come from the corona. For these reasons, the equations of this model were applied to the results of the spectral analysis. Using this model, the mass accretion rates, the mass evaporation rates, and the radii of the coronas were calculated to be ~10-12.3-10-11.3 M⊙ yr -1, ~10-6.5-10-5.5 g cm -2 s -1 and ~109.1-109.9 cm , respectively. The pressures in the coronas were less than ~1200 g cm -2 s -1 for (z) up to ~10×109 cm . The obtained values suggest that the Corona model can indeed operate in SU UMa type Dwarf Novae.

scholarly journals Effects of radiation in accretion regions of classical T Tauri stars

2019 ◽  
Vol 629 ◽  
pp. L9 ◽  
Author(s):  
S. Colombo ◽  
L. Ibgui ◽  
S. Orlando ◽  
R. Rodriguez ◽  
G. Espinosa ◽  
...  
Keyword(s):  
Thermal Conduction ◽  
Thermal Structure ◽  
Radiation Hydrodynamics ◽  
Shock Heating ◽  
T Tauri ◽  
Shock Region ◽  
Accretion Rates ◽  
Post Shock ◽  
Effects Of Radiation ◽  
The Impact

Context. Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns where optically thin and thick plasma components coexist. Thus, an accurate description of these impacts is necessary to account for the effects of absorption and emission of radiation. Aims. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock down-falling material. We investigate whether a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. Methods. We developed a radiation hydrodynamics model describing an accretion column impacting onto the surface of a classical T Tauri star. The model takes into account the stellar gravity, the thermal conduction, and the effects of radiative losses and of absorption of radiation by matter in the nonlocal thermodynamic equilibrium regime. Results. After the impact, a hot slab of post-shock plasma develops at the base of the accretion column. Part of the radiation emerging from the slab is absorbed by the pre-shock accreting material. As a result, the pre-shock accretion column gradually heats up to temperatures of 105 K, forming a radiative precursor of the shock. The precursor has a thermal structure with the hottest part at T ≈ 105 K, with a size comparable to that of the hot slab, above the post-shock region. At larger distances the temperature gradually decreases to T ≈ 104 K. Conclusions. Our model predicts that ≈70% of the radiation emitted by the post-shock plasma is absorbed by the pre-shock accretion column immediately above the slab and is re-emitted in the UV band. This may explain why accretion rates derived from UV observations are systematically higher than rates inferred from X-ray observations.

scholarly journals Global 3D radiation-hydrodynamic simulations of gas accretion: Opacity-dependent growth of Saturn-mass planets

2019 ◽  
Vol 632 ◽  
pp. A118 ◽  
Author(s):  
M. Schulik ◽  
A. Johansen ◽  
B. Bitsch ◽  
E. Lega
Keyword(s):  
Gas Flow ◽  
Temporal Evolution ◽  
Accretion Rate ◽  
Hydrodynamic Simulations ◽  
Accretion Flow ◽  
Accretion Rates ◽  
Energy Sink ◽  
Dependent Growth ◽  
Self Gravity ◽  
Gas Accretion

The full spatial structure and temporal evolution of the accretion flow into the envelopes of growing gas giants in their nascent discs is only accessible in simulations. Such simulations are constrained in their approach of computing the formation of gas giants by dimensionality, resolution, consideration of self-gravity, energy treatment and the adopted opacity law. Our study explores how a number of these parameters affect the measured accretion rate of a Saturn-mass planet. We present a global 3D radiative hydrodynamics framework using the FARGOCA-code. The planet is represented by a gravitational potential with a smoothing length at the location of the planet. No mass or energy sink is used; instead luminosity and gas accretion rates are self-consistently computed. We find that the gravitational smoothing length must be resolved by at least ten grid cells to obtain converged measurements of the gas accretion rates. Secondly, we find gas accretion rates into planetary envelopes that are compatible with previous studies, and continue to explain those via the structure of our planetary envelopes and their luminosities. Our measured gas accretion rates are formally in the stage of Kelvin–Helmholtz contraction due to the modest entropy loss that can be obtained over the simulation timescale, but our accretion rates are compatible with those expected during late run-away accretion. Our detailed simulations of the gas flow into the envelope of a Saturn-mass planet provide a framework for understanding the general problem of gas accretion during planet formation and highlight circulation features that develop inside the planetary envelopes. Those circulation features feedback into the envelope energetics and can have further implications for transporting dust into the inner regions of the envelope.

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