Cosmic rays: extragalactic and Galactic

From the analysis of the flux of high energy particles, $E>3cdot 10^{18}eV$, it is shown that the distribution of the power density of extragalactic rays over energy is of the power law, ${bar q}(E)propto E^{-2.7}$, with the same index of $2.7$ that has the distribution of Galactic cosmic rays before so called knee, $E<3cdot 10^{15}eV$. However, the average power of extragalactic sources, which is of ${cal E}simeq 10^{43}erg ,s^{-1}$, at least two orders exceeds the power emitted by the Galaxy in cosmic rays, assuming that the density of galaxies is estimated as $N_gsimeq 1 Mpc^{-3}$. Considering that such power can be provided by relativistic jets from active galactic nuclei with the power ${cal E}simeq 10^{45} - 10^{46} erg , s^{-1}$, we estimate the density of extragalactic sources of cosmic rays as $N_gsimeq 10^{-2}-10^{-3}, Mpc^{-3}$. Assuming the same nature of Galactic and extragalactic rays, we conclude that the Galactic rays were produced by a relativistic jet emitted from the Galactic center during the period of its activity in the past. The remnants of a bipolar jet are now observed in the form of bubbles of relativistic gas above and below the Galactic plane. The break, observed in the spectrum of Galactic rays (knee), is explained by fast escape of energetic particle, $E>3cdot 10^{15}eV$, from the Galaxy because of the dependence of the coefficient of diffusion of cosmic rays on energy, $Dpropto E^{0.7}$. The obtained index of the density distribution of particles over energy, $N(E)propto E^{-2.7-0.7/2}=E^{-3.05}$, for $E>3cdot 10^{15}eV$ agrees well with the observed one, $N(E)propto E^{-3.1}$. Estimated time of termination of the jet in the Galaxy is $4.2cdot 10^{4}$ years ago.

On the collective curvature radiation

The paper deals with the one possible mechanism of the pulsar radio emission, i.e., with the collective curvature radiation of the relativistic particle stream moving along the curved magnetospheric magnetic field lines. It is shown that the electromagnetic wave containing one cylindrical harmonic exp{is{phi}} can not be radiated by the curvature radiation mechanism, that corresponds to radiation of a charged particle moving along curved magnetic field lines. The point is that the particle in vacuum radiates the triplex of harmonics (s, s pm 1), so for the collective curvature radiation the wave polarization is very important and cannot be fixed a priori. For this reason the polarization of real unstable waves must be determined directly from the solution of wave equations for the media. Its electromagnetic properties should be described by the dielectric permittivity tensor ^{epsilon}({omega},k,r), that contains the information on the reaction on all possible types of radiation.

Absorption of Gamma-Ray Photons in a Vacuum Neutron Star Magnetosphere: II. The Formation of Lightnings

The absorption of a high-energy photon from the external cosmic gamma-ray background in the inner neutron star magnetosphere triggers the generation of a secondary electron-positron plasma and gives rise to a lightning - a lengthening and simultaneously expanding plasma tube. It propagates along magnetic fields lines with a velocity close to the speed of light. The high electron-positron plasma generation rate leads to dynamical screening of the longitudinal electric field that is provided not by charge separation but by electric current growth in the lightning. The lightning radius is comparable to the polar cap radius of a radio pulsar. The number of electron-positron pairs produced in the lightning in its lifetime reaches 10^28. The density of the forming plasma is comparable to or even higher than that in the polar cap regions of ordinary pulsars. This suggests that the radio emission from individual lightnings can be observed. Since the formation time of the radio emission is limited by the lightning lifetime, the possible single short radio bursts may be associated with rotating radio transients (RRATs).

Absorption of Gamma-Ray Photons in a Vacuum Neutron Star Magnetosphere: I. Electron-Positron Pair Production

The production of electron-positron pairs in a vacuum neutron star magnetosphere is investigated for both low (compared to the Schwinger one) and high magnetic fields. The case of a strong longitudinal electric field where the produced electrons and positrons acquire a stationary Lorentz factor in a short time is considered. The source of electron-positron pairs has been calculated with allowance made for the pair production by curvature and synchrotron photons. Synchrotron photons are shown to make a major contribution to the total pair production rate in a weak magnetic field. At the same time, the contribution from bremsstrahlung photons may be neglected. The existence of a time delay due to the finiteness of the electron and positron acceleration time leads to a great reduction in the electron-positron plasma generation rate compared to the case of a zero time delay. The effective local source of electron-positron pairs has been constructed. It can be used in the hydrodynamic equations that describe the development of a cascade after the absorption of a photon from the cosmic gamma-ray background in a neutron star magnetosphere.

On the origin of galactic cosmic rays

It is shown that the relativistic jet, emitted from the center of the Galaxy during its activity, possessed power and energy spectrum of accelerated protons sufficient to explain the current cosmic rays distribution in the Galaxy. Proton acceleration takes place on the light cylinder surface formed by the rotation of a massive black hole carring into rotation the radial magnetic field and the magnetosphere. Observed in gamma, x-ray and radio bands bubbles above and below the galactic plane can be remnants of this bipolar get. The size of the bubble defines the time of the jets start, $simeq 2.4cdot 10^7$ years ago. The jet worked more than $10^7$ years, but less than $2.4cdot10^7$ years.

Electron-Positron Plasma Generation in a Magnetar Magnetosphere

We consider the electron-positron plasma generation processes in the magnetospheres of magnetars - neutron stars with strong surface magnetic fields, B = 10^(14) - 10^(15) G. We show that the photon splitting in a magnetic field, which is effective at large field strengths, does not lead to the suppression of plasma multiplication, but manifests itself in a high polarization of gamma-ray photons. A high magnetic field strength does not give rise to the second generation of particles produced by synchrotron photons. However, the density of the first-generation particles produced by curvature photons in the magnetospheres of magnetars can exceed the density of the same particles in the magnetospheres of ordinary radio pulsars. The plasma generation inefficiency can be attributed only to slow magnetar rotation, which causes the energy range of the produced particles to narrow. We have found a boundary in the P - Pdot diagram that defines the plasma generation threshold in a magnetar magnetosphere.

The Filling of Neutron Star Magnetospheres with Plasma: Dynamics of the Motion of Electrons and Positrons

We consider the motion of charged particles in the vacuum magnetospheres of rotating neutron stars with a strong surface magnetic field, B>10^(12) G. The electrons and positrons falling into the magnetosphere or produced in it are shown to be captured by the force-free surface EB=0. Using the Dirac-Lorentz equation, we investigate the dynamics of particle capture and subsequent motion near the force-free surface. The particle energy far from the force-free surface has been found to be determined by the balance between the power of the forces of an accelerating electric field and the intensity of curvature radiation. When captured, the particles perform adiabatic oscillations along the magnetic field lines and simultaneously move along the force-free surface. We have found the oscillation parameters and trajectories of the captured particles. We have calculated the characteristic capture times and energy losses of the particles through the emission of both bremsstrahlung and curvature photons by them. The capture of particles is shown to lead to a monotonic increase in the thickness of the layer of charged plasma accumulating near the force-free surface. The time it takes for a vacuum magnetosphere to be filled with plasma has been estimated.