S.V. Bogovalov

Abrupt acceleration of a /`cold/' ultrarelativistic wind from the Crab pulsar

Pulsars are thought to eject electron–positron winds that energize the surrounding environment, with the formation of a pulsar wind nebula. The pulsar wind originates close to the light cylinder, the surface at which the pulsar co-rotation velocity equals the speed of light, and carries away much of the rotational energy lost by the pulsar. Initially the wind is dominated by electromagnetic energy (Poynting flux) but later this is converted to the kinetic energy of bulk motion. It is unclear exactly where this takes place and to what speed the wind is accelerated. Although some preferred models imply a gradual acceleration over the entire distance from the magnetosphere to the point at which the wind terminates, a rapid acceleration close to the light cylinder cannot be excluded. Here we report that the recent observations of pulsed, very high-energy γ-ray emission from the Crab pulsar are explained by the presence of a cold (in the sense of the low energy of the electrons in the frame of the moving plasma) ultrarelativistic wind dominated by kinetic energy. The conversion of the Poynting flux to kinetic energy should take place abruptly in the narrow cylindrical zone of radius between 20 and 50 light-cylinder radii centred on the axis of rotation of the pulsar, and should accelerate the wind to a Lorentz factor of (0.5–1.0) × 106. Although the ultrarelativistic nature of the wind does support the general model of pulsars, the requirement of the very high acceleration of the wind in a narrow zone not far from the light cylinder challenges current models.

TeV light curve of PSR B1259–63/SS2883

The inverse Compton scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63/SS2883. While this process can explain the energy spectrum of the observed TeV emission, the detected gamma-ray fluxes do not agree with the published theoretical predictions of the TeV lightcurve. The main objective of this paper is to show that the HESS results can be explained, under certain reasonable assumptions, by inverse Compton scenarios of gamma-ray production in the system. In this paper we study evolution of the energy spectra of relativistic electrons under different assumptions about the acceleration and energy-loss rates of electrons, and the impact of these processes on the lightcurve of IC gamma-rays. We demonstrate that the observed TeV lightcurve can be explained (i) by adiabatic losses which dominate over the entire trajectory of the pulsar with a significant increase towards the periastron, or (ii) by the sub-TeV cutoffs in the energy spectra of electrons due to the enhanced rate of Compton losses close to the periastron. The Compton deceleration of the pulsar wind contributes to the decrease of the nonthermal power released in the accelerated electrons, and thus to the reduction of the IC and synchrotron components of radiation close to the periastron. Although this effect alone cannot explain the observed lightcurves, the Comptonization of the pulsar wind leads to the formation of gamma-radiation with a line-type energy spectrum. While the HESS data already constrain the Lorentz factor of the wind,

RAPID TeV VARIABILITY IN BLAZARS AS A RESULT OF JET-STAR INTERACTION

\Gamma \le 10^6

Modelling interaction of relativistic and non-relativistic winds in binary system PSR B1259-63/SS2883 - II. Impact of magnetization and anisotropy of the pulsar wind

, future observations of this object with GLAST should allow a deep probe of the wind Lorentz factor in the range between

Magnetocentrifugal acceleration of bulk motion of plasma in pulsar magnetosphere

10^4

On a Formula to Evaluate the Separative Power of Long Gas Centrifuges

and

Verification of software codes for simulation of unsteady flows in a gas centrifuge

10^6

TeV light curve of PSR B1259-63/SS2883: TeV light curve of PSR B1259-63/SS2883

.

Waves in strong centrifugal fields: dissipationless gas

We propose a new model for the description of ultra-short flares from TeV blazars by compact magnetized condensations (blobs), produced when red giant stars cross the jet close to the central black hole. Our study includes a simple dynamic model for the evolution of the envelope lost by the star in the jet and its high-energy nonthermal emission through different leptonic and hadronic radiation mechanisms. We show that the fragmented envelope of the star can be accelerated to Lorentz factors up to 100 and effectively radiate the available energy in gamma rays predominantly through proton synchrotron radiation or external inverse Compton scattering of electrons. The model can readily explain the minute-scale TeV flares on top of longer (typical timescales of days) gamma-ray variability as observed from the blazar PKS 2155–304. In the framework of the proposed scenario, the key parameters of the source are robustly constrained. In the case of proton synchrotron origin of the emission, a mass of the central black hole of M BH ≈ 108 M ☉, a total jet power of L j ≈ 2 × 1047 erg s–1, and a Doppler factor of the gamma-ray emitting blobs of δ ≥ 40 are required. For the external inverse Compton model, parameters of M BH ≈ 108 M ☉, L j ≈ 1046 erg s–1, and δ ≥ 150 are required.

Gamma-ray flares from red giant/jet interactions in AGN

In this paper, we present a numerical study of the properties of the flow produced by the collision of a magnetized anisotropic pulsar wind with its environment in binary system. We compare the impact of both the magnetic field and the wind anisotropy to the benchmark case of a purely hydrodynamical (HD) interaction of isotropic winds, which has been studied in detail by Bogovalov et al. (2008). We consider the interaction in axisymmetric approximation, i.e. the pulsar rotation axis is assumed to be oriented along the line between the pulsar and the optical star and the effects related to the pulsar orbiting are neglected. The impact of the magnetic field is studied for the case of weak magnetization (with magnetization parameter