Papers by Serguei Komissarov
The strong variability of magnetic central engines of AGN and GRBs may result in highly intermitt... 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
Modeling the time variability of Pulsaw Wind Nebulae
It is known that PWNe show a short time variability at high energies. Variability of the wisps in... 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
On the linear stability of sheared and magnetized jets without current sheets – non-relativistic case
Monthly Notices of the Royal Astronomical Society, 2016
Computational Astrophysics and Cosmology, 2015
Monthly Notices of the Royal Astronomical Society, 2015
We model the inner knot of the Crab Nebula as a synchrotron emission coming from the non-spherica... more We model the inner knot of the Crab Nebula as a synchrotron emission coming from the non-spherical MHD termination shock of relativistic pulsar wind. The post-shock flow is mildly relativistic; as a result the Doppler-beaming has a strong impact on the shock appearance. The model can reproduce the knot location, size, elongation, brightness distribution, luminosity and polarization provided the effective magnetization of the section of the pulsar wind producing the knot is low, σ ≤ 1. In the striped wind model, this implies that the striped zone is rather wide, with the magnetic inclination angle of the Crab pulsar ≥ 45 • ; this agrees with the previous model-dependent estimate based on the gamma-ray emission of the pulsar. We conclude that the tiny knot is indeed a bright spot on the surface of a quasi-stationary magnetic relativistic shock and that this shock is a site of efficient particle acceleration. On the other hand, the deduced low magnetization of the knot plasma implies that this is an unlikely site for the Crab's gamma-ray flares, if they are related to the fast relativistic magnetic reconnection events.
Relativistic blastwaves accelerate particles which are scattered by a highly disordered magnetic ... 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.
The strong dependence of the neutrino annihilation mechanism on the mass accretion rate makes it ... 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.
The paper describes an explicit multi-dimensional numerical scheme for Special Relativistic Two-F... 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.
Self-similar solutions for a poloidal magnetic field in a turbulent jet
The evolution of a large-scale magnetic field in a turbulent jet in an extragalactic radio source... more The evolution of a large-scale magnetic field in a turbulent jet in an extragalactic radio source is examined. Self-similar solutions are found for a weak poloidal magnetic field transported by a turbulent jet of incompressible fluid. It is shown that the radial profiles of these solutions are the eigenfunctions of a linear differential operator. The evolution of a large-scale magnetic field is strongly dependent on the field's configuration. It is concluded that the observed magnetic field of extragalactic radio jets can be represented by the small-scale anisotropic field generated by turbulence inside the jets.
VLA maps of total intensity and fractional polarization at 3.6 cm are presented foreleven radio g... 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
This is a brief review of the recent developments in the theory of magnetic acceleration of relat... 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.
Exploring the Gamma Ray Universe, Sep 1, 2001
We present simulations of the complete evolution of a fireball model for gamma ray bursts using a... 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.
A New Mechanism of Hypernovae Explosions
We present numerical simulations of axisymmetric, magnetically driven relativistic jets. To elimi... 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 $R\ga 10^{16} {\rm cm}$.
Monthly Notices of the Royal Astronomical Society, 2014
In this paper we discuss the development of Rayleigh-Taylor filaments in axisymmetric simulations... more In this paper we discuss the development of Rayleigh-Taylor filaments in axisymmetric simulations of Pulsar wind nebulae (PWN). High-resolution adaptive mesh refinement magnetohydrodynamic (MHD) simulations are used to resolve the non-linear evolution of the instability. The typical separation of filaments is mediated by the turbulent flow in the nebula and hierarchical growth of the filaments. The strong magnetic dissipation and field-randomization found in recent global three-dimensional simulations of PWN suggests that magnetic tension is not strong enough to suppress the growth of RT filaments, in agreement with the observations of prominent filaments in the Crab nebula. The long-term axisymmetric results presented here confirm this finding.
International Journal of Modern Physics D, 2008
MVB) and [email protected] (SSK) We present numerical simulations of cold, axisymmetric, ... more MVB) and [email protected] (SSK) We present numerical simulations of cold, axisymmetric, magnetically driven relativistic outflows. The outflows are initially sub-Alfvénic and Poynting flux-dominated, with total-to-rest-mass energy flux ratio up to µ ∼ 620. To study the magnetic acceleration of jets we simulate flows confined within a funnel with rigid wall of prescribed shape, which we take to be z ∝ r a (in cylindrical coordinates, with a ranging from 1 to 2). This allows us to eliminate the numerical dissipative effects induced by a free boundary with an ambient medium. We find that in all cases they converge to a steady state characterized by a spatially extended acceleration region. For the jet solutions the acceleration process is very efficient -on the outermost scale of the simulation more than half of the Poynting flux has been converted into kinetic energy flux, and the terminal Lorentz factor approached its maximum possible value (Γ∞ ≃ µ). The acceleration is accompanied by the collimation of magnetic field lines in excess of that dictated by the funnel shape. The numerical solutions are generally consistent with the semi-analytic self-similar jets solutions and the spatially extended acceleration observed in some astrophysical relativistic jets. In agreement with previous studies we also find that the acceleration is significantly less effective for wind solutions suggesting that pulsar winds may remain Poynting dominated when they reach the termination shock.
AIP Conference Proceedings, 2009
In this study we explore the magnetic mechanism of hypernovae and relativistic jets of long durat... more In this study we explore the magnetic mechanism of hypernovae and relativistic jets of long duration gamma ray bursts within the collapsar scenario. This is an extension of our earlier work . We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state and takes into account the cooling associated with emission of neutrinos and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe solutions with different black hole rotation, mass accretion rate, and strength of progenitor's magnetic field. Some of them exhibits strong explosions driven by Poyntingdominated jets with power up to 12 × 10 51 erg s −1 . These jets originate from the black hole and powered via the Blandford-Znajek mechanism. A provisional criterion for explosion is derived. A number of simulation movies can be downloaded from
Models of Quasars
Astrophysics and Space Science Library, 2012
ABSTRACT At present, it is believed that all or most galaxies harbor a massive or even supermassi... 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.
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Papers by Serguei Komissarov