Advection schemes for capturing relativistic shocks with high Lorentz factors

Jet-plasmas emanating from the vicinity of relativistic objects and in gamma-ray bursts have been observed to propagate with Lorentz factors laying in the range between one and several hundreds. On the other hand, the numerical studies of such flows have been focused so far mainly on the lowest possible range of Lorentz factors Γ, specifically, on the regime 1 ≤ Γ ≤ 5. Therefore, relativistic flows with high Γ− factors have poorly studied, as most numerical methods are found to encounter severe numerical difficulties or even become numerically unstable for Γ >> 1. In this paper we present an implicit numerical advection scheme for modeling the propagation of relativistic plasmas with shocks, discuss its consistency with respect to both the internal and total energy formulation in general relativity. Using the total energy formulation, the scheme is found to be viable for modeling moving shocks with moderate Lorentz factors, though with relatively small Courant numbers. In the limit of high Lorentz factors, the internal energy formulation in combination with a fine-tuned artificial viscosity is much more robust and efficient. We confirm our conclusions by performing test calculations and compare the results with analytical solutions of the relativistic shock tube problem. The aim of the present modification is to enhance the robustness of the general relativistic implicit radiative MHD solver: GR-I-RMHD (http://www1.iwr.uni-heidelberg.de/groups/compastro/home/gr-i-mhdsolver) and extend its range of applications into the high Γ− regime.

Advection schemes for capturing relativistic shocks with high Lorentz factors

Jet-plasmas emanating from the vicinity of relativistic objects and in gamma-ray bursts have been observed to propagate with Lorentz factors laying in the range between one and several hundreds. On the other hand, the numerical studies of such flows have been focused so far mainly on the lowest possible range of Lorentz factors Γ, specifically, on the regime 1 ≤ Γ ≤ 5. Therefore, relativistic flows with high Γ− factors have poorly studied, as most numerical methods are found to encounter severe numerical difficulties or even become numerically unstable for Γ >> 1. In this paper we present an implicit numerical advection scheme for modeling the propagation of relativistic plasmas with shocks, discuss its consistency with respect to both the internal and total energy formulation in general relativity. Using the total energy formulation, the scheme is found to be viable for modeling moving shocks with moderate Lorentz factors, though with relatively small Courant numbers. In the limit of high Lorentz factors, the internal energy formulation in combination with a fine-tuned artificial viscosity is much more robust and efficient. We confirm our conclusions by performing test calculations and compare the results with analytical solutions of the relativistic shock tube problem. The aim of the present modification is to enhance the robustness of the general relativistic implicit radiative MHD solver: GR-I-RMHD (http://www1.iwr.uni-heidelberg.de/groups/compastro/home/gr-i-mhdsolver) and extend its range of applications into the high Γ− regime.

Launching proton-dominated jets from accreting Kerr Black Holes: the case of M87

A general relativistic model for the formation and acceleration of low mass-loaded jets from systems containing accreting black holes is presented. The model is based on previous numerical results and theoretical studies in the Newtonian regime, but modified to include the effects of space-time curvature in the vicinity of the event horizon of a spinning black hole. It is argued that the boundary layer between the Keplerian accretion disk and the event horizon is best suited for the formation and acceleration of the accretion-powered jets in active galactic nuclei and micro-quasars. The model presented here is based on matching the solutions of three different regions: i- a weakly magnetized Keplerian accretion disk in the outer part, where the transport of angular momentum is mediated through the magentorotational instability, ii- a strongly magnetized, advection-dominated and turbulent-free boundary layer (BL) between the outer cold accretion disk and the event horizon and where the plasma rotates sub-Keplerian and iii- a transition zone (TZ) between the BL and the overlying corona, where the electrons and protons are thermally uncoupled, highly dissipative and rotate super-Keplerian. In the BL, the gravitation-driven dynamical collapse of the plasma increases the strength of the poloidal magnetic field (PMF) significantly, subsequently suppressing the generation and dissipation of turbulence and turning off the primary source of heating. In this case, the BL appears much fainter than standard disk models so as if the disk truncates at a certain radius. The action of the PMF in the BL is to initiate torsional Alf`ven waves that transport angular momentum from the embedded plasma vertically into the TZ, where a significant fraction of the shear-generated toroidal magnetic field reconnects, thereby heating the protons up to the virial-temperature. Also, the strong PMF forces the electrons to cool rapidly, giving rise therefore to the formation of a gravitationally unbound two-temperature proton-dominated outflow. Our model predicts the known correlation between the Lorentz-factor and the spin parameter of the BH. It also shows that the effective surface of the BL, through which the baryons flow into the TZ, shrinks with increasing the spin parameter, implying therefore that low mass-loaded jets most likely originate from around Kerr black holes. When applying our model to the jet in the elliptical galaxy M87, we find a spin parameter <em>a ∈</em> [0.99, 0.998], a transition radius rtr ≈ 30 gravitational radii and a fraction of 0.05 − 0.1 of the mass accretion rate goes into the TZ, where the plasma speeds up its outward-oriented motion to reach a Lorentz factor Γ <em>∈</em> [2.5, 5.0] at rtr.

Launching proton-dominated jets from accreting Kerr Black Holes: the case of M87

A general relativistic model for the formation and acceleration of low mass-loaded jets from systems containing accreting black holes is presented. The model is based on previous numerical results and theoretical studies in the Newtonian regime, but modified to include the effects of space-time curvature in the vicinity of the event horizon of a spinning black hole. It is argued that the boundary layer between the Keplerian accretion disk and the event horizon is best suited for the formation and acceleration of the accretion-powered jets in active galactic nuclei and micro-quasars. The model presented here is based on matching the solutions of three different regions: i- a weakly magnetized Keplerian accretion disk in the outer part, where the transport of angular momentum is mediated through the magentorotational instability, ii- a strongly magnetized, advection-dominated and turbulent-free boundary layer (BL) between the outer cold accretion disk and the event horizon and where the plasma rotates sub-Keplerian and iii- a transition zone (TZ) between the BL and the overlying corona, where the electrons and protons are thermally uncoupled, highly dissipative and rotate super-Keplerian. In the BL, the gravitation-driven dynamical collapse of the plasma increases the strength of the poloidal magnetic field (PMF) significantly, subsequently suppressing the generation and dissipation of turbulence and turning off the primary source of heating. In this case, the BL appears much fainter than standard disk models so as if the disk truncates at a certain radius. The action of the PMF in the BL is to initiate torsional Alf`ven waves that transport angular momentum from the embedded plasma vertically into the TZ, where a significant fraction of the shear-generated toroidal magnetic field reconnects, thereby heating the protons up to the virial-temperature. Also, the strong PMF forces the electrons to cool rapidly, giving rise therefore to the formation of a gravitationally unbound two-temperature proton-dominated outflow. Our model predicts the known correlation between the Lorentz-factor and the spin parameter of the BH. It also shows that the effective surface of the BL, through which the baryons flow into the TZ, shrinks with increasing the spin parameter, implying therefore that low mass-loaded jets most likely originate from around Kerr black holes. When applying our model to the jet in the elliptical galaxy M87, we find a spin parameter a ∈ [0.99, 0.998], a transition radius rtr ≈ 30 gravitational radii and a fraction of 0.05 − 0.1 of the mass accretion rate goes into the TZ, where the plasma speeds up its outward-oriented motion to reach a Lorentz factor Γ ∈ [2.5, 5.0] at rtr.

Launching proton-dominated jets from accreting Kerr Black Holes: the case of M87

A general relativistic model for the formation and acceleration of low mass-loaded jets from systems containing accreting black holes is presented. The model is based on previous numerical results and theoretical studies in the Newtonian regime, but modified to include the effects of space-time curvature in the vicinity of the event horizon of a spinning black hole. It is argued that the boundary layer between the Keplerian accretion disk and the event horizon is best suited for the formation and acceleration of the accretion-powered jets in active galactic nuclei and micro-quasars. The model presented here is based on matching the solutions of three different regions: i- a weakly magnetized Keplerian accretion disk in the outer part, where the transport of angular momentum is mediated through the magentorotational instability, ii- a strongly magnetized, advection-dominated and turbulent-free boundary layer (BL) between the outer cold accretion disk and the event horizon and where the plasma rotates sub-Keplerian and iii- a transition zone (TZ) between the BL and the overlying corona, where the electrons and protons are thermally uncoupled, highly dissipative and rotate super-Keplerian. In the BL, the gravitation-driven dynamical collapse of the plasma increases the strength of the poloidal magnetic field (PMF) significantly, subsequently suppressing the generation and dissipation of turbulence and turning off the primary source of heating. In this case, the BL appears much fainter than standard disk models so as if the disk truncates at a certain radius. The action of the PMF in the BL is to initiate torsional Alf`ven waves that transport angular momentum from the embedded plasma vertically into the TZ, where a significant fraction of the shear-generated toroidal magnetic field reconnects, thereby heating the protons up to the virial-temperature. Also, the strong PMF forces the electrons to cool rapidly, giving rise therefore to the formation of a gravitationally unbound two-temperature proton-dominated outflow. Our model predicts the known correlation between the Lorentz-factor and the spin parameter of the BH. It also shows that the effective surface of the BL, through which the baryons flow into the TZ, shrinks with increasing the spin parameter, implying therefore that low mass-loaded jets most likely originate from around Kerr black holes. When applying our model to the jet in the elliptical galaxy M87, we find a spin parameter a ∈ [0.99, 0.998], a transition radius rtr ≈ 30 gravitational radii and a fraction of 0.05 − 0.1 of the mass accretion rate goes into the TZ, where the plasma speeds up its outward-oriented motion to reach a Lorentz factor Γ ∈ [2.5, 5.0] at rtr.

The effects of the Moon's shadow and pre-shadow on the artificial satellites motion

The perturbations due to the solar radiation pressure forces on the Earth's artificial satellites have been given taking into account the Moon's shadow and pre-shadow effects. The formulae are convenient when the perturbed forces are obtained by numerical methods. The study shows that the cylindrical model of the shadow is insufficient and that the conic shadow model including the pre-shadow gives more accurate results.

The effects of the Moon's shadow and pre-shadow on the artificial satellites motion

The perturbations due to the solar radiation pressure forces on the Earth's artificial satellites have been given taking into account the Moon's shadow and pre-shadow effects. The formulae are convenient when the perturbed forces are obtained by numerical methods. The study shows that the cylindrical model of the shadow is insufficient and that the conic shadow model including the pre-shadow gives more accurate results.

The effects of the Moon's shadow and pre-shadow on the artificial satellites motion

The perturbations due to the solar radiation pressure forces on the Earth's artificial satellites have been given taking into account the Moon's shadow and pre-shadow effects. The formulae are convenient when the perturbed forces are obtained by numerical methods. The study shows that the cylindrical model of the shadow is insufficient and that the conic shadow model including the pre-shadow gives more accurate results.<br />

Welcome to a new, international open-access research journal with a particular focus on the development of theoretical and experimental techniques and methodology

I have recently had the privilege of being appointed Editor-in-Chief of this very exciting and innovative Open Access Journal, and hereby extend a warm welcome to everyone as we launch Astronomy Studies Development, which will seek to publish high quality, peer-reviewed, original manuscripts in all fields of astronomy and astrophysics, though with a particular focus on mathematical techniques and methodology and innovative ideas for instrumental development and modeling in astronomy and astrophysics. The journal will also seek to publish simulations in all areas, including cosmology, particle astrophysics, accretion, and diffuse media. Our journal will include both full length research articles and letter articles, and its coverage extends over solar, stellar, galactic and extragalactic astronomy and astrophysics, and will report original research in all wavelength bands. Astronomy and Astrophysics are rather mature disciplines, with a history of quality journals over the past century or more. So one may reasonably ask why a new journal such as this is needed. Obviously, I myself have answered this question in the affirmative. After a long career in research and publishing, I have the perspective to provide several good reasons for helping to promote the evolution of publishing in Astronomy and Astrophysics to a place more in line with present technology..........

Welcome to a new, international open-access research journal with a particular focus on the development of theoretical and experimental techniques and methodology

I have recently had the privilege of being appointed Editor-in-Chief of this very exciting and innovative Open Access Journal, and hereby extend a warm welcome to everyone as we launch Astronomy Studies Development, which will seek to publish high quality, peer-reviewed, original manuscripts in all fields of astronomy and astrophysics, though with a particular focus on mathematical techniques and methodology and innovative ideas for instrumental development and modeling in astronomy and astrophysics. The journal will also seek to publish simulations in all areas, including cosmology, particle astrophysics, accretion, and diffuse media. Our journal will include both full length research articles and letter articles, and its coverage extends over solar, stellar, galactic and extragalactic astronomy and astrophysics, and will report original research in all wavelength bands. Astronomy and Astrophysics are rather mature disciplines, with a history of quality journals over the past century or more. So one may reasonably ask why a new journal such as this is needed. Obviously, I myself have answered this question in the affirmative. After a long career in research and publishing, I have the perspective to provide several good reasons for helping to promote the evolution of publishing in Astronomy and Astrophysics to a place more in line with present technology..........