Reinhard Schlickeiser

Nonthermal Compton and Synchrotron Processes in the Jets of Active Galactic Nuclei

We present the basic equations for calculating the time-dependent received spectral flux from the optically thin emissivities produced by temporally evolving, nonthermal electrons losing energy in a relativistically moving blob of plasma located at cosmological distances. Ionization, bremsstrahlung, Compton, and synchrotron energy losses of the electrons are considered. These equations are used to derive and calculate the received spectral fluence produced by instantaneously injected nonthermal electrons that also scatter photons from an isotropic external monochromatic radiation field in the Thomson regime of scattering. The derivation of the fluences is restricted to the regime where either synchrotron losses or Thomson losses with photons of the external radiation field dominate the electron energy loss rate. We also derive approximate expressions for the synchrotron and synchrotron self-Compton fluence. Beaming factors for thin-target and thick-target models of the electron distributions are derived. We show that ionization energy losses of relativistic electrons on the background thermal plasma of the blob can give Comptonized gamma-ray fluence spectra with spectral breaks Δα 0.5. If only Thomson and synchrotron losses are important, spectral breaks 0.5 are also possible if electrons are injected with a low-energy cutoff or if a snapshot of the spectral flux is measured over a time interval much less than the interval during which electrons cool. The important observational quantities for testing Compton-scattering models of radio galaxies and blazars are the bolometric luminosities in the radio/optical synchrotron component and the X-ray/γ-ray Compton component, which approximately equal the peak values of the νFν spectral power flux or fluence. Numerical simulations of jet spectra are presented, showing the effects of different parameter values on the shapes of the synchrotron and Compton components. We derive straightforward predictions for the simplest external Compton and synchrotron self-Compton models from the analytic expressions for the spectra. The results are applied to quasi-simultaneous observations of 3C 279 at two different epochs, showing that this behavior can be understood if the blazar radiation results from electrons that Compton-scatter externally produced photons in outflowing blobs with different bulk Lorentz factors. Fits to quasi-simultaneous observations of 3C 273 and quiescent and flaring states of Mrk 421 are also presented.

Quasi-linear Theory of Cosmic Ray Transport and Acceleration: The Role of Oblique Magnetohydrodynamic Waves and Transit-Time Damping

We calculate quasi-linear transport and acceleration parameters for cosmic ray particles interacting resonantly with undamped fast-mode waves propagating in a low-β plasma. For super-Alfvenic particles and a vanishing cross-helicity state of the fast-mode waves, we demonstrate that the rate of adiabatic deceleration vanishes, and that the momentum and spatial diffusion coefficients can be calculated from the Fokker-Planck coefficient Dμμ. Adopting isotropic fast-mode turbulence with a Kolmogorov-like turbulence spectrum, we demonstrate that Dμμ is the sum of contributions from transit-time damping and gyroresonant interactions. Gyroresonance refers to | n | ≠ 0 resonant particle-wave interactions. Transit-time damping refers to the n = 0 interaction of particles with the compressive magnetic field component of the fast-mode waves. We show that transit-time damping provides the dominant contribution to pitch-angle scattering in the interval ≤ | μ | ≤ 1, where is the ratio of Alfven to particle speed. In the interval | μ | < , transit-time damping does not occur, and gyroresonance provides a small but finite contribution to particle scattering. As a consequence, the momentum diffusion coefficient is mainly determined by the transit-time damping contribution. On the other hand, since the spatial diffusion coefficient and the related mean free path are given by the average over μ of the inverse of Dμμ, these spatial transport parameters are determined by the contribution from the interval | μ | < . We also calculate the cosmic ray transport parameters for plasma turbulence consisting of a mixture of isotropic fast-mode waves and slab Alfven waves. Here, the momentum diffusion coefficient is determined by the transit-time damping of the fast-mode waves, and is a factor ln -1 larger than in the case of pure slab Alfven wave turbulence. The mean free path and the spatial diffusion coefficient are modified significantly from the pure fast-mode case, since the crucial scattering at | μ | < is now provided by gyroresonances with slab Alfven waves. The mean free path is a constant at nonrelativistic energies, and may account for the legendary λfit-λQLT discrepancy of solar energetic particles.

Quasars, Blazars, and Gamma Rays

Before the launch of the Compton Gamma Ray Observatory (CGRO), the only source of >100-megaelectron volt (MeV) gamma radiation known outside our galaxy was the quasar 3C 273. After less than a year of observing, 13 other extragalactic sources have been discovered with the Energetic Gamma Ray Experiment Telescope (EGRET) on CGRO, and it is expected that many more will be found before the full sky survey is complete. All 14 sources show evidence of blazar properties at other wavelengths; these properties include high optical polarization, extreme optical variability, flat-spectrum radio emission associated with a compact core, and apparent superluminal motion. Such properties are thought to be produced by those few, rare extragalactic radio galaxies and quasars that are favorably aligned to permit us to look almost directly down a relativistically outflowing jet of matter expelled from a supermassive black hole. Although the origin of the gamma rays from radio jets is a subject of much controversy, the gamma-ray window probed by CGRO is providing a wealth of knowledge about the central engines of active galactic nuclei and the most energetic processes occurring in nature.

Relativistic kinetic theory of waves in isotropic plasmas

The properties of longitudinal and transverse oscillations in isotropic unmagnetized plasmas of arbitrary composition are investigated on the basis of the Maxwell equations and the relativistic Vlasov equation. We show that in such plasmas (i) superluminal longitudinal and transverse waves undergo no collisionless Landau damping; and (ii) all isotropic particle distributions functions are stable against the excitation of longitudinal and transverse waves. Specializing to the textbook example of longitudinal fluctuations in a pure-electron equilibrium plasma, we derive various analytical expressions for the longitudinal dispersion relation valid for any value of the electron plasma temperature characterized by the dimensionless parameter μ = m e c 2 /k B T e , which allow simpler approximations for non-relativistic (μ >> 1) and ultrarelativistic (μ > 1 can be expressed in terms of the Fried and Conte plasma dispersion function, but does not agree with the earlier results of Landau, Jackson and others, which were calculated starting from the non-relativistic form of the Vlasov-Maxwell equations. We establish a significant difference in the argument of the plasma dispersion function. This difference only shows up because we have started from a relativistically correct formulation of the kinetic theory, and it profoundly influences the results for the real and imaginary part of the frequency also for non-relativistic plasma temperatures. We show that the non-relativistic limit of the longitudinal dispersion relation reduces to the Landau-Jackson form only if the (unphysical) limit of an infinitely large value of the speed of light c → ∞ is taken.

Longitudinal oscillations in hot isotropic Maxwellian plasmas

Using the relativistic Vlasov equation and the appropriate Maxwell–Boltzmann–Juttner distribution for the unperturbed plasma thermal equilibrium state, it is demonstrated that the longitudinal dispersion relation in warm isotropic Maxwellian plasmas has two real roots with superluminal phase speed below a characteristic wave number kc that is determined by the plasma frequency and the plasma temperature. The superluminal oscillations undergo no Landau damping. The relativistically correct analysis leads to markedly different results than previous nonrelativistic work which incorrectly yielded a nonzero imaginary part of the roots for all phase speeds.

The Beaming Pattern of Doppler-boosted Thermal Annihilation Radiation: Application to MeV Blazars

The beaming pattern of thermal annihilation radiation is broader than the beaming pattern produced by isotropic nonthermal electrons and positrons in the jets of radio-emitting active galactic nuclei that Compton scatter photons from an external isotropic radiation field. Thus, blueshifted thermal annihilation radiation can provide the dominant contribution to the high-energy radiation spectrum at observing angles θ 1/Γ, where Γ is the bulk Lorentz factor of the outflowing plasma. This effect may account for the spectral features of MeV blazars discovered with the Compton Telescope on the Compton Gamma Ray Observatory. Coordinated gamma-ray observations of annihilation line radiation to infer Doppler factors and VLBI radio observations to measure transverse angular speeds of outflowing plasma blobs can be used to determine the Hubble constant.

On The Location of the Acceleration and Emission Sites in Gamma-Ray Blazars

Compton scattering of external radiation by nonthermal particles in outflowing blazar jets is dominated by accretion-disk photons rather than scattered radiation to distances

On Landau damping in hot equilibrium plasmas. I. Longitudinal oscillations along an external magnetic field

sim 0.01-0.1

Three-dimensional models of a galactic wind expansion with ellipsoidal geometry. I - The hydrodynamical test case

pc from the central engine for standard parameters, thus clarifying the limits of validity of the model by the present authors and the model of Sikora, Begelman, & Rees. On the basis of contemporaneous Ginga X-ray and EGRET gamma-ray observations, we estimate the radius of 3C 279s gamma-ray photosphere to be smaller than estimated by Blandford. There is thus no need to require that the acceleration and emission sites of gamma-ray blazars to be located farther than

On the dispersion relation of longitudinal waves in equilibrium plasmas

sim 10^{2-3}