Zaza Osmanov

On the efficiency of particle acceleration by rotating magnetospheres in AGN

Aims. To investigate the efficiency of centrifugal acceleration of particles as a possible mechanism for the generation of ultra-high γ-ray nonthermal emission from TeV blazars, we study the centrifugal acceleration of electrons by rotating magnetic field lines, for an extended range of inclination angles and determine the maximum Lorentz factors γmax attainable by the electrons via this process. Methods. Two principal limiting mechanisms for the particle acceleration, inverse Compton scattering and breakdown of the beadon-the-wire approximation, are examined. Results. Particles may be centrifugally accelerated up to γmax � 10 8 and the main limiting mechanism for the γmax is the inverse Compton scattering. Conclusions. The energy of centrifugally accelerated particles can be amply sufficient for the generation (via inverse Compton scattering) of the ultra-high energy (up to 20 TeV) gamma emission in TeV blazars.

Parametric mechanism of the rotation energy pumping by a relativistic plasma

An investigation of the kinematics of a plasma stream rotating in the pulsar magnetosphere is presented. On the basis of an exact set of equations describing the behavior of the plasma stream, the increment of the instability is obtained, and the possible relevance of this approach for the understanding of the pulsar rotation energy pumping mechanism is discussed.

Centrifugally Driven Relativistic Dynamics on Curved Trajectories

Motion of test particles along rotating curved trajectories is considered. The problem is studied both in the laboratory and the rotating frames of reference. It is assumed that the system rotates with the constant angular velocity ω = const. The solutions are found and analyzed for the case when the form of the trajectory is given by an Archimedes spiral. It is found that particles can reach infinity while they move along these trajectories and the physical interpretation of their behaviour is given. The analogy of this idealized study with the motion of particles along the curved rotating magnetic field lines in the pulsar magnetosphere is pointed out. We discuss further physical development (the conserved total energy case, when ω ≠ const) and astrophysical applications (the acceleration of particles in active galactic nuclei) of this theory.

On particle acceleration and very high energy γ-ray emission in Crab-like pulsars

Context. The origin of very energetic charged particles and the production of very high-energy (VHE) gamma-ray emission remains still a challenging issue in modern pulsar physics. Aims. By applying a toy model, we explore the acceleration of co-rotating charged particles close to the light surface in a plasma-rich pulsar magnetosphere and study their interactions with magnetic and photon fields under conditions appropriate for Crab-type pulsars. Methods. Centrifugal acceleration of particles in a monopol-like magnetic field geometry is analyzed and the efficiency constraints, imposed by corotation, inverse Compton interactions and curvature radiation reaction are determined. We derive expressions for the maximum particle energy and provide estimates for the corresponding high-energy curvature and inverse Compton power outputs. Results. It is shown that for Crab-like pulsars, electron Lorentz factor up to γ ∼ 10 7 can be achieved, allowing inverse Compton (Klein-Nishina) up-scattering of thermal photons to TeV energies with a maximum luminosity output of ∼10 31 erg/s. Curvature radiation, on the other hand, will result in a strong GeV emission output of up to ∼(10 34 −10 35 )e rg/s, quasi-exponentially decreasing towards higher energies for photon energies below ∼50 GeV. Conclusions. Accordingly to the results presented only young pulsars are expected to be sites of detectable VHE γ-ray emission.

Ultra High Energy Electrons Powered by Pulsar Rotation

A new mechanism of particle acceleration, driven by the rotational slow down of the Crab pulsar, is explored. The rotation, through the time dependent centrifugal force, can efficiently excite unstable Langmuir waves in the electron-positron (hereafter e±) plasma of the star magnetosphere. These waves, then, Landau damp on electrons accelerating them in the process. The net transfer of energy is optimal when the wave growth and the Landau damping times are comparable and are both very short compared to the star rotation time. We show, by detailed calculations, that these are precisely the conditions for the parameters of the Crab pulsar. This highly efficient route for energy transfer allows the electrons in the primary beam to be catapulted to multiple TeV (~ 100 TeV) and even PeV energy domain. It is expected that the proposed mechanism may, unravel the puzzle of the origin of ultra high energy cosmic ray electrons.

Dynamical feedback of the curvature drift instability on its saturation process

Aims. We investigate the reconstruction of pulsar magnetospheres close to the light cylinder surface to study the curvature drift instability (CDI) responsible for the twisting of magnetic field lines in the mentioned zone. The influence of plasma dynamics on the saturation process of the CDI is studied. Methods. On the basis of the Euler, continuity, and induction equations, we derive the increment of the CDI and analyze parametrically excited drift modes. The dynamics of the reconstruction of the pulsar magnetosphere is studied analytically. Results. We show that there is a possibility of a parametrically excited rotational-energy pumping-process in the drift modes. It is indicated by the generation of a toroidal component of the magnetic field that transforms the field lines into such a configuration, in which plasma particles do not experience any forces. At this stage, the instability process saturates and the further amplification of the toroidal component to the magnetic field lines is suspended.

ON THE VERY HIGH ENERGY SPECTRUM OF THE CRAB PULSAR

In the present paper, we construct a self-consistent theory interpreting the observations from the MAGIC Cherenkov Telescope of the very high energy (VHE) pulsed emission from the Crab pulsar. In particular, on the basis of Vlasovs kinetic equation, we study the process of quasi-linear diffusion (QLD) developed by means of the cyclotron instability. This mechanism provides simultaneous generation of low (radio) and VHE (0.01-25 GeV) emission on light cylinder scales in one location of the pulsar magnetosphere. A different approach to the synchrotron emission is considered, giving the spectral index of the VHE emission ({beta} = 2) and the exponential cutoff energy (23 GeV) in good agreement with the observational data.

On the Very High Energy Pulsed Emission in the Crab Pulsar

We have examined the recently detected very high energy (VHE) pulsed radiation from the Crab pulsar. According to the observational evidence, the observed emission (>25GeV) peaks at the same phase with the optical spectrum. Considering the cyclotron instability, we show that the pitch angle becomes non-vanishing leading to the efficient synchrotron mechanism near the light cylinder surface. The corresponding spectral index of the emission equals -1/2. By studying the inverse Compton scattering and the curvature radiation, it is argued that the aforementioned mechanisms do not contribute to the VHE radiation detected by MAGIC.

On the Simultaneous Generation of High-energy Emission and Submillimeter/Infrared Radiation from Active Galactic Nuclei

For active galactic nuclei (AGNs) we study the role of the mechanism of quasi-linear diffusion (QLD) in producing the high energy emission in the MeV-GeV domains strongly connected with the submillimeter/infrared radiation. Considering the kinetic equation governing the stationary regime of the QLD we investigate the feedback of the diffusion on electrons. We show that this process leads to the distribution of particles by the pitch angles, implying that the synchrotron mechanism is no longer prevented by energy losses. Examining a reasonable interval of physical parameters, we show that it is possible to produce MeV-GeV gamma-rays, strongly correlated with submillimeter/infrared bands.

Centrifugally driven electrostatic instability in extragalactic jets

The stability problem of the rotation-induced electrostatic wave in extragalactic jets is presented. Solving a set of equations describing dynamics of a relativistic plasma flow of active galactic nuclei (AGN) jets, an expression of the instability rate has been derived and analyzed for typical values of AGNs. The growth rate was studied versus the wavelength and the inclination angle and it has been found that the instability process is very efficient with respect to the accretion disk evolution, indicating high efficiency of the instability.