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Kei Kotake - One of the best experts on this subject based on the ideXlab platform.
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Dependence of the Outer Boundary Condition on protoneutron star asteroseismology with gravitational-wave signatures
Physical Review D, 2019Co-Authors: Hajime Sotani, Takami Kuroda, Tomoya Takiwaki, Kei KotakeAbstract:To obtain the eigenfrequencies of a protoneutron star (PNS) in the postbounce phase of core-collapse supernovae (CCSNe), we perform a linear perturbation analysis of the angle-averaged PNS profiles using results from a general relativistic CCSN simulation of a $15 M_{\odot}$ star. In this work, we investigate how the choice of the Outer Boundary Condition could affect the PNS oscillation modes in the linear analysis. By changing the density at the Outer Boundary of the PNS surface in a parametric manner, we show that the eigenfrequencies strongly depend on the surface density. By comparing with the gravitational wave (GW) signatures obtained in the hydrodynamics simulation, the so-called surface $g$-mode of the PNS can be well ascribed to the fundamental oscillations of the PNS. The frequency of the fundamental oscillations can be fitted by a function of the mass and radius of the PNS similar to the case of cold neutron stars. In the case that the position of the Outer Boundary is chosen to cover not only the PNS but also the surrounding postshock region, we obtain the eigenfrequencies close to the modulation frequencies of the standing accretion-shock instability (SASI). However, we point out that these oscillation modes are unlikely to have the same physical origin of the SASI modes seen in the hydrodynamics simulation. We discuss possible limitations of applying the angle-averaged, linear perturbation analysis to extract the full ingredients of the CCSN GW signatures.
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Dependence of the Outer Boundary Condition on protoneutron star asteroseismology with gravitational-wave signatures
Physical Review D, 2019Co-Authors: Hajime Sotani, Takami Kuroda, Tomoya Takiwaki, Kei KotakeAbstract:To obtain the eigenfrequencies of a protoneutron star (PNS) in the postbounce phase of core-collapse supernovae (CCSNe), we perform a linear perturbation analysis of the angle-averaged PNS profiles using results from a general relativistic CCSN simulation of a $15\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ star. In this work, we investigate how the choice of the Outer Boundary Condition could affect the PNS oscillation modes in the linear analysis. By changing the density at the Outer Boundary of the PNS surface in a parametric manner, we show that the eigenfrequencies strongly depend on the surface density. By comparing with the gravitational wave (GW) signatures obtained in the hydrodynamics simulation, the so-called surface $g$-mode of the PNS can be well ascribed to the fundamental oscillations of the PNS. The frequency of the fundamental oscillations can be fitted by a function of the mass and radius of the PNS similar to the case of cold neutron stars. In the case that the position of the Outer Boundary is chosen to cover not only the PNS but also the surrounding postshock region, we obtain the eigenfrequencies close to the modulation frequencies of the standing accretion-shock instability (SASI). However, we point out that these oscillation modes are unlikely to have the same physical origin of the SASI modes seen in the hydrodynamics simulation. We discuss possible limitations of applying the angle-averaged, linear perturbation analysis to extract the full ingredients of the CCSN GW signatures.
Hajime Sotani - One of the best experts on this subject based on the ideXlab platform.
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Dependence of the Outer Boundary Condition on protoneutron star asteroseismology with gravitational-wave signatures
Physical Review D, 2019Co-Authors: Hajime Sotani, Takami Kuroda, Tomoya Takiwaki, Kei KotakeAbstract:To obtain the eigenfrequencies of a protoneutron star (PNS) in the postbounce phase of core-collapse supernovae (CCSNe), we perform a linear perturbation analysis of the angle-averaged PNS profiles using results from a general relativistic CCSN simulation of a $15 M_{\odot}$ star. In this work, we investigate how the choice of the Outer Boundary Condition could affect the PNS oscillation modes in the linear analysis. By changing the density at the Outer Boundary of the PNS surface in a parametric manner, we show that the eigenfrequencies strongly depend on the surface density. By comparing with the gravitational wave (GW) signatures obtained in the hydrodynamics simulation, the so-called surface $g$-mode of the PNS can be well ascribed to the fundamental oscillations of the PNS. The frequency of the fundamental oscillations can be fitted by a function of the mass and radius of the PNS similar to the case of cold neutron stars. In the case that the position of the Outer Boundary is chosen to cover not only the PNS but also the surrounding postshock region, we obtain the eigenfrequencies close to the modulation frequencies of the standing accretion-shock instability (SASI). However, we point out that these oscillation modes are unlikely to have the same physical origin of the SASI modes seen in the hydrodynamics simulation. We discuss possible limitations of applying the angle-averaged, linear perturbation analysis to extract the full ingredients of the CCSN GW signatures.
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Dependence of the Outer Boundary Condition on protoneutron star asteroseismology with gravitational-wave signatures
Physical Review D, 2019Co-Authors: Hajime Sotani, Takami Kuroda, Tomoya Takiwaki, Kei KotakeAbstract:To obtain the eigenfrequencies of a protoneutron star (PNS) in the postbounce phase of core-collapse supernovae (CCSNe), we perform a linear perturbation analysis of the angle-averaged PNS profiles using results from a general relativistic CCSN simulation of a $15\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ star. In this work, we investigate how the choice of the Outer Boundary Condition could affect the PNS oscillation modes in the linear analysis. By changing the density at the Outer Boundary of the PNS surface in a parametric manner, we show that the eigenfrequencies strongly depend on the surface density. By comparing with the gravitational wave (GW) signatures obtained in the hydrodynamics simulation, the so-called surface $g$-mode of the PNS can be well ascribed to the fundamental oscillations of the PNS. The frequency of the fundamental oscillations can be fitted by a function of the mass and radius of the PNS similar to the case of cold neutron stars. In the case that the position of the Outer Boundary is chosen to cover not only the PNS but also the surrounding postshock region, we obtain the eigenfrequencies close to the modulation frequencies of the standing accretion-shock instability (SASI). However, we point out that these oscillation modes are unlikely to have the same physical origin of the SASI modes seen in the hydrodynamics simulation. We discuss possible limitations of applying the angle-averaged, linear perturbation analysis to extract the full ingredients of the CCSN GW signatures.
Arnab K. Ray - One of the best experts on this subject based on the ideXlab platform.
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Critical properties of spherically symmetric accretion in a fractal medium
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Nirupam Roy, Arnab K. RayAbstract:Spherically symmetric transonic accretion of a fractal medium has been studied in both the stationary and the dynamic regimes. The stationary transonic solution is greatly sensitive to infinitesimal deviations in the Outer Boundary Condition, but the flow becomes transonic and stable when its evolution is followed through time. The evolution towards transonicity is more pronounced for a fractal medium than it is for a continuum, and in the former case the static sonic Condition is met on relatively larger length scales. The dynamic approach also shows that there is a remarkable closeness between an equation of motion for a perturbation in the flow, and the metric of an analogue acoustic black hole. The stationary inflow solutions of a fractal medium are as much stable under the influence of linearized perturbations as they are for the fluid continuum.
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Hydraulic jump in one-dimensional flow
The European Physical Journal B, 2005Co-Authors: Subhendu B. Singha, Jayanta K. Bhattacharjee, Arnab K. RayAbstract:In the presence of viscosity the hydraulic jump in one dimension is seen to be a first-order transition. A scaling relation for the position of the jump has been determined by applying an averaging technique on the stationary hydrodynamic equations. This gives a linear height profile before the jump, as well as a clear dependence of the magnitude of the jump on the Outer Boundary Condition. The importance of viscosity in the jump formation has been convincingly established, and its physical basis has been understood by a time-dependent analysis of the flow equations. In doing so, a very close correspondence has been revealed between a perturbation equation for the flow rate and the metric of an acoustic white hole. We finally provide experimental support for our heuristically developed theory.
Feng Yuan - One of the best experts on this subject based on the ideXlab platform.
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The role of the Outer Boundary Condition in accretion disk models
AIP Conference Proceedings, 2001Co-Authors: Feng Yuan, Qiuhe Peng, Jianmin WangAbstract:Taking optically thin accretion flows as an example, we investigate the effects of the Outer Boundary Condition (OBC) on the dynamics and the emergent spectra of accretion flows. We find that OBC plays an important role. This is because the accretion equations describing the behavior of accretion flows are a set of differential equations, therefore, accretion is intrinsically an initial-value problem. The result means that we should seriously consider the initial physical state of the accretion flow such as its angular momentum and its temperature. An application example to Sgr A* is presented.
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the role of the Outer Boundary Condition in accretion disk models theory and application
arXiv: Astrophysics, 2000Co-Authors: Feng Yuan, Qiuhe Peng, Jianmin WangAbstract:The influence of the Outer Boundary Condition (OBC) on the dynamics and radiation of optically thin accretion flow is investigated. Bremsstrahlung and synchrotron radiations amplified by Comptonization are taken into account and two-temperature plasma assumption is adopted. The three OBCs we adopted are the temperatures of the electrons and ions and the specific angular momentum of the accretion flow at a certain Outer Boundary. We find that when the general parameters such as the mass accretion rate and the viscous parameter are fixed, the peak flux at various bands such as radio, IR and X-ray, can differ by as large as several orders of magnitude under different OBCs in our example. Our results indicate that OBC is both dynamically and radiatively important therefore should be regarded as a new ``parameter'' in accretion disk models. We apply the above results to the compact radio source Sgr A* and find that the discrepancy between the mass accretion rate favored by ADAF models in the literature and that favored by the three dimensional hydrodynamical simulation can be naturally resolved by seriously considering the Outer Boundary Condition of the accretion flow.
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The Role of the Outer Boundary Condition in Accretion Disk Models: Theory and Application
The Astrophysical Journal, 2000Co-Authors: Feng Yuan, Qiuhe Peng, Jianmin WangAbstract:In a previous paper, we find that the Outer Boundary Conditions (OBCs) of an optically thin accretion flow play an important role in determining the structure of the flow. Here in this paper, we further investigate the influence of OBCs on the dynamics and radiation of the accretion how on a more detailed level. Bremsstrahlung and synchrotron radiations amplified by Comptonization are taken into account, and two-temperature plasma assumption is adopted. The three OBCs we adopted are the temperatures of the electrons and ions and the specific angular momentum of the accretion flow at a certain Outer Boundary. We investigate the individual role of each of the three OBCs on the dynamical structure and the emergent spectrum. We find that when the general parameters such as the mass accretion rate M and the viscous parameter alpha are fixed the peak flux at various bands such as radio, IR, and X-ray can differ by as much as several orders of magnitude under different OBCs in our example. Our results indicate that the OBC is both dynamically and radiatively important and therefore should be regarded as a new "parameter" in accretion disk models. As an illustrative example, we further apply the above results to the compact radio source Sgr A* located at the center of our Galaxy. The advection-dominated accretion flow (ADAF) model has turned out to be a great success in explaining its luminosity and spectrum. However, there exists a discrepancy between the mass accretion rate favored by ADAF models in the literature and that favored by the three-dimensional hydrodynamical simulation, with the former being 10-20 times smaller than the latter. By seriously considering the Outer Boundary Condition of the accretion flow, we find that because of the low specific angular momentum of the accretion gas the accretion in Sgr A* should belong to a new accretion pattern, which is characterized by the possession of a very large sonic radius. This accretion pattern can significantly reduce the discrepancy between the mass accretion rates. We argue that the accretion occurred in some detached binary systems; the core of nearby elliptical galaxies and active galactic nuclei very possibly belongs to this accretion pattern.
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Accretion Flows: The Role of the Outer Boundary Condition
The Astrophysical Journal, 1999Co-Authors: Feng YuanAbstract:We investigate the influences of the Outer Boundary Conditions on the structure of an optically thin accretion flow. We find that the Outer Boundary Condition plays an important role in determining the topological structure and the profiles of the density and temperature of the solutions. Therefore, it should be regarded as a new parameter in the accretion model.
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accretion flows the role of the Outer Boundary Condition
arXiv: Astrophysics, 1999Co-Authors: Feng YuanAbstract:We investigate the influences of the Outer Boundary Conditions(OBCs) on the structure of an optically thin accretion flow. We find that OBC plays an important role in determining the topological structure and the profiles of the surface density and temperature of the solution, therefore it should be regarded as a new parameter in the accretion disk model.
Daniel Proga - One of the best experts on this subject based on the ideXlab platform.
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time evolution of the three dimensional accretion flows effects of the adiabatic index and Outer Boundary Condition
The Astrophysical Journal, 2009Co-Authors: Agnieszka Janiuk, Maciej Sznajder, Monika Mościbrodzka, Daniel ProgaAbstract:We study a slightly rotating accretion flow onto a black hole, using the fully three-dimensional (3D) numerical simulations. We consider hydrodynamics of an inviscid flow, assuming a spherically symmetric density distribution at the Outer Boundary and a small, latitude-dependent angular momentum. We investigate the role of the adiabatic index and gas temperature, and the flow behavior due to non-axisymmetric effects. Our 3D simulations confirm axisymmetric results: the material that has too much angular momentum to be accreted forms a thick torus near the equator, and the mass accretion rate is lower than the Bondi rate. In our previous study of the 3D accretion flows, for γ = 5/3, we found that the inner torus precessed, even for axisymmetric Conditions at large radii. The present study shows that the inner torus precesses also for other values of the adiabatic index: γ = 4/3, 1.2, and 1.01. However, the time for the precession to set increases with decreasing γ. In particular, for γ = 1.01, we find that depending on the Outer Boundary Conditions, the torus may shrink substantially due to the strong inflow of the non-rotating matter, and the precession will have insufficient time to develop. On the other hand, if the torus is supplied by the continuous inflow of the rotating material from the Outer radii, its inner parts will eventually tilt and precess, as was for the larger γ's.
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time evolution of the 3 d accretion flows eects of the adiabatic index and Outer Boundary Condition
arXiv: High Energy Astrophysical Phenomena, 2009Co-Authors: Agnieszka Janiuk, Maciej Sznajder, Daniel ProgaAbstract:We study a slightly rotating accretion ow onto a black hole, using the fully three dimensional (3-D) numerical simulations. We consider hydrodynamics of an inviscid ow, assuming a spherically symmetric density distribution at the Outer Boundary and a small, latitude-dependent angular momentum. We investigate the role of the adiabatic index and gas temperature, and the ow behaviour due to non-axisymmetric eects. Our 3-D simulations conrm axisymmetric results: the material that has too much angular momentum to be accreted forms a thick torus near the equator and the mass accretion rate is lower than the Bondi rate. In our previous study of the 3-D accretion ows, for = 5=3, we found that the inner torus precessed, even for axisymmetric Conditions at large radii. The present study shows that the inner torus precesses also for other values of the adiabatic index: = 4=3; 1:2, and 1.01. However, the time for the precession to set increases with decreasing . In particular, for = 1:01 we nd that depending on the Outer Boundary Conditions, the torus may shrink substantially due to the strong inow of
