The strong variability of magnetic central engines of AGN and GRBs may result in highly intermittent strongly magnetized relativistic outflows. We find a new magnetic acceleration mechanism for such impulsive flows that can be much more... more
The strong variability of magnetic central engines of AGN and GRBs may result in highly intermittent strongly magnetized relativistic outflows. We find a new magnetic acceleration mechanism for such impulsive flows that can be much more effective than the acceleration of steady-state flows. This impulsive acceleration results in kinetic-energy-dominated flows at astrophysically relevant distances from the central source. For a
Research Interests:
It is known that PWNe show a short time variability at high energies. Variability of the wisps in the Crab Nebula has long been known, the jet in Vela appears to be strongly variable, and B1509 shows also variability in the inner ring.... more
It is known that PWNe show a short time variability at high energies. Variability of the wisps in the Crab Nebula has long been known, the jet in Vela appears to be strongly variable, and B1509 shows also variability in the inner ring. Variability in the jet, which usually has timescale of years, on the other hand the wisps show
Research Interests:
Relativistic blastwaves accelerate particles which are scattered by a highly disordered magnetic field. These particles are then advected downstream of the shock where they emit synchrotron radiation in the ambient magnetic field. We have... more
Relativistic blastwaves accelerate particles which are scattered by a highly disordered magnetic field. These particles are then advected downstream of the shock where they emit synchrotron radiation in the ambient magnetic field. We have developed a numerical code to study the hydrodynamics of a strong relativistic blastwave with a general equation of state. We study the acceleration of particles by the forward and reverse shocks and solve for their emission. Implications for the fireball model of gamma ray bursts are discussed.
Research Interests:
Research Interests:
The strong dependence of the neutrino annihilation mechanism on the mass accretion rate makes it difficult to explain the LGRBs with duration in excess of 100 seconds as well as the precursors separated from the main gamma-ray pulse by... more
The strong dependence of the neutrino annihilation mechanism on the mass accretion rate makes it difficult to explain the LGRBs with duration in excess of 100 seconds as well as the precursors separated from the main gamma-ray pulse by few hundreds of seconds. Even more difficult is to explain the Swift observations of the shallow decay phase and X-ray flares, if they indeed indicate activity of the central engine for as long as 10,000 seconds. These data suggest that some other, most likely magnetic mechanisms have to be considered. The magnetic models do not require the development of accretion disk within the first few seconds of the stellar collapse and hence do not require very rapidly rotating stellar cores at the pre-supernova state. This widens the range of potential LGRB progenitors. In this paper, we re-examine the close binary scenario allowing for the possibility of late development of accretion disks in the collapsar model and investigate the available range of mass accretion rates, black hole masses, and spins. A particularly interesting version of the binary progenitor involves merger of a WR star with an ultra-compact companion, neutron star or black hole. In this case we expect the formation of very long-lived accretion disks, that may explain the phase of shallow decay and X-ray flares observed by Swift. Similarly long-lived magnetic central engines are expected in the current single star models of LGRB progenitors due to their assumed exceptionally fast rotation.
Research Interests:
The paper describes an explicit multi-dimensional numerical scheme for Special Relativistic Two-Fluid Magnetohydrodynamics of electron-positron plasma and a suit of test problems. The scheme utilizes Cartesian grid and the third order... more
The paper describes an explicit multi-dimensional numerical scheme for Special Relativistic Two-Fluid Magnetohydrodynamics of electron-positron plasma and a suit of test problems. The scheme utilizes Cartesian grid and the third order WENO interpolation. The time integration is carried out using the third order TVD method of Runge-Kutta type, thus ensuring overall third order accuracy on smooth solutions. The magnetic field is kept near divergence-free by means of the method of generalized Lagrange multiplier. The test simulations, which include linear and non-linear continuous plasma waves, shock waves, strong explosions and the tearing instability, show that the scheme is sufficiently robust and confirm its accuracy.
VLA maps of total intensity and fractional polarization at 3.6 cm are presented foreleven radio galaxies, part of a sample of 29 nearby radio galaxies with P 178 ? 1:5 \Theta1025W Hz\Gamma1sr\Gamma1. Ten have classical double structure.... more
VLA maps of total intensity and fractional polarization at 3.6 cm are presented foreleven radio galaxies, part of a sample of 29 nearby radio galaxies with P 178 ? 1:5 \Theta1025W Hz\Gamma1sr\Gamma1. Ten have classical double structure. The hotspots in all of theseare well resolved. We have discovered a one-sided jet in 3C 135, as well as imaging theknown jets
Research Interests:
Research Interests:
This is a brief review of the recent developments in the theory of magnetic acceleration of relativistic jets. We attempt to explain the key results of this complex theory using basic physical arguments and simple calculations. The main... more
This is a brief review of the recent developments in the theory of magnetic acceleration of relativistic jets. We attempt to explain the key results of this complex theory using basic physical arguments and simple calculations. The main focus is on the standard model, which describes steady-state axisymmetric ideal MHD flows. We argue that this model is over-restrictive and discuss various alternatives.
Research Interests:
We present simulations of the complete evolution of a fireball model for gamma ray bursts using a relativistic hydrodynamic code. Particle acceleration at both the forward and reverse shocks produces energetic electrons which then emit... more
We present simulations of the complete evolution of a fireball model for gamma ray bursts using a relativistic hydrodynamic code. Particle acceleration at both the forward and reverse shocks produces energetic electrons which then emit synchrotron radiation in the ambient magnetic field. The observed synchrotron spectrum is calculated.
Research Interests:
We present numerical simulations of axisymmetric, magnetically driven relativistic jets. To eliminate the dissipative effects induced by a free boundary with an ambient medium we assume that the flow is confined by a rigid wall of a... more
We present numerical simulations of axisymmetric, magnetically driven relativistic jets. To eliminate the dissipative effects induced by a free boundary with an ambient medium we assume that the flow is confined by a rigid wall of a prescribed shape, which we take to be $z\propto r^a$ (in cylindrical coordinates, with $a$ ranging from 1 to 3). The outflows are initially cold, sub-Alfv\'enic and Poynting flux-dominated, with a total--to--rest-mass energy flux ratio $\mu \sim 15$. We find that in all cases they converge to a steady state characterized by a spatially extended acceleration region. The acceleration process is very efficient: on the outermost scale of the simulation as much as $\sim 77%$ of the Poynting flux has been converted into kinetic energy flux, and the terminal Lorentz factor approaches its maximum possible value ($\Gamma_\infty \simeq \mu$). We also find a high collimation efficiency: all our simulated jets develop a cylindrical core. We argue that this could be the rule for current-carrying outflows that start with a low initial Lorentz factor ($\Gamma_0 \sim 1$). Our conclusions on the high acceleration and collimation efficiencies are not sensitive to the particular shape of the confining boundary or to the details of the injected current distribution, and they are qualitatively consistent with the semi-analytic self-similar solutions derived by Vlahakis & K\"onigl. We apply our results to the interpretation of relativistic jets in AGNs: we argue that they naturally account for the spatially extended accelerations inferred in these sources ($\Gamma_\infty \ga 10$ attained on radial scales $R\ga 10^{17} {\rm cm}$) and are consistent with the transition to the matter-dominated regime occurring already at $R\ga 10^{16} {\rm cm}$.
Research Interests:
Research Interests:
Research Interests:
ABSTRACT At present, it is believed that all or most galaxies harbor a massive or even supermassive black hole in their nuclei. Sometimes gas finds its way close to and finally into the black hole. This process of accretion is thought to... more
ABSTRACT At present, it is believed that all or most galaxies harbor a massive or even supermassive black hole in their nuclei. Sometimes gas finds its way close to and finally into the black hole. This process of accretion is thought to give rise to an active galactic nucleus and in extreme cases, a quasar. The most widely considered model then involves a black hole, an accretion disk, an obscuring torus (for unification), and, for radio-loud sources, very powerful relativistic radio jets.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Black Holes, High Energy Density Physics, Numerical Method, Magnetic field, Accretion Disks, and 14 moreBlack Hole Physics, Cosmology, Models, General, Energetics, Gamma Ray Burst, Black Hole, Accretion Discs, Collapse, Magnetic Fields, MHD, Rotational energy, Magnetic Flux, and Strong magnetic field
Research Interests:
Research Interests: Magnetohydrodynamics, Active Galactic Nuclei, Numerical Method, Accretion Disks, Numerical Simulation, and 13 morePower Law, Gamma Ray Burst, Light curves, Analytical Solution, Accretion Discs, Kinetic Energy, Active Galaxies, MHD, Magnetization, Indexation, Gamma Ray, Pressure Distribution, and Conversion Efficiency
Research Interests:
Research Interests:
Research Interests: Magnetohydrodynamics, Equations of State, Numerical Method, Magnetic field, Neutrino, and 23 moreModels, Variability, Plasma, Oscillations, Gamma Ray Burst, Collapse, Magnetic Fields, MHD, Numerical Model, Three Dimensional, Magnetization, Rotational energy, Flow Velocity, Energy Transfer, Large Scale, Jet, Gamma Ray, Total Energy, Equation of State, Neutrinos, Massless Particles, Gamma Emission, and Gamma radiation
Research Interests:
Research Interests: Black Holes, Magnetic field, Neutrino, Accretion Disks, Black Hole Physics, and 17 moreCosmology, X Rays, Numerical Simulation, Gamma Ray Burst, Black Hole, Accretion Discs, Collapse, Magnetic Fields, MHD, Jet, Gamma Ray, Elementary Particles, Neutrinos, Massless Particles, Gamma radiation, Magnetic Flux, and Strong magnetic field
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
VLA maps of total intensity and fractional polarization at lambda3.6 cm are presented for 11 radio galaxies, part of a sample of 29 nearby radio galaxies with P_178>1.5x10^25WHz^-1sr^-1. Ten have classical double structure. The hotspots... more
VLA maps of total intensity and fractional polarization at lambda3.6 cm are presented for 11 radio galaxies, part of a sample of 29 nearby radio galaxies with P_178>1.5x10^25WHz^-1sr^-1. Ten have classical double structure. The hotspots in all of these are well resolved. We have discovered a one-sided jet in 3C 135, as well as imaging the known jets in 3C 98, 111 and 445 at high resolution. There are also possible jets in five of the remaining six classical doubles. The eleventh object, 3C 15, is well imaged here for the first time. It is dominated by a bright jet, and a weak counterjet is also detected. We point out some of the more common patterns in the structure of the hotspot complexes in our sample, and summarize the frequency with which jets and the various types of hotspot complex are found.