Felix Spanier

Simplified Models for Photohadronic Interactions in Cosmic Accelerators

We discuss simplified models for photo-meson production in cosmic accelerators, such as active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). Our self-consistent models are directly based on the underlying physics used in the SOPHIA software and can be easily adapted if new data are included. They allow for the efficient computation of neutrino and photon spectra (from π0 decays) as a major requirement of modern time-dependent simulations of the astrophysical sources and parameter studies. In addition, the secondaries (pions and muons) are explicitly generated, a necessity if cooling processes are to be included. For the neutrino production, we include the helicity dependence of the muon decays which in fact leads to larger corrections than the details of the interaction model. The separate computation of the π0, π+, and π– fluxes allows, for instance, for flavor ratio predictions of the neutrinos at the source, which are a requirement of many tests of neutrino properties using astrophysical sources. We confirm that for charged pion generation, the often used production by the Δ(1232)-resonance is typically not the dominant process in AGNs and GRBs, and we show, for arbitrary input spectra, that the number of neutrinos are underestimated by at least a factor of two if they are obtained from the neutral-to-charged pion ratio. We compare our results for several levels of simplification using isotropic synchrotron and thermal spectra and demonstrate that they are sufficiently close to the SOPHIA software.

Modelling the steady state spectral energy distribution of the BL-Lac Object PKS 2155-30.4 using a selfconsistent SSC model

In this paper we present a fully selfconsistent SSC model with particle acceleration due to shock and stochastic acceleration (Fermi-I and Fermi-II-Processes re- spectively) to model the quiescent spectral energy distribu- tion (SED) observed from PKS 2155. The simultaneous August/September 2008 multiwavelength data of H.E.S.S., Fermi, RXTE/SWIFT and ATOM give new constraints to the high-energy peak in the SED concerning its curvature. We find that, in our model, a monoenergetic injection of electrons at 0=910 into the model region, which are ac- celerated by Fermi-I- and Fermi-II-processes while suffering synchrotron and inverse Compton losses, finally leads to the observed SED of PKS 2155-30.4 shown in H. E. S. S. and Fermi-LAT collaborations (2009). In contrast to other SSC models our parameters arise from the jets microphysics and the spectrum is evolving selfconsistently from diffusion and acceleration. The 0-factor can be interpreted as two coun- terstreaming plasmas due to the motion of the blob at a bulk factor of 0=58 and opposed moving upstream electrons at moderate Lorentz factors with an average of u 8.

A self-consistent and time-dependent hybrid blazar emission model

A time-dependent emission model for blazar jets, taking acceleration due to Fermi-I and Fermi-II processes for electrons and protons as well as all relevant radiative processes self-consistently into account, is presented. The presence of highly relativistic protons within the jet extends the simple synchrotron self-Compton case not only in the very high energy radiation of blazars, but also in the X-ray regime, introducing non-linear behaviour in the emitting region of the model by photon-meson production and emerging electron positron pair cascades. We are able to investigate the variability patterns of blazars in terms of our model in all energy bands, thus narrowing down the parameters used. The blazar 1 ES 1011+496 serves as an example of how this model is applied to high frequency peaked BL Lac Objects in the presence of non-thermal protons within the jet. Typical multiband patterns are derived, which are experimentally accessible.

Emission of Type II Radio Bursts - Single-Beam versus Two-Beam Scenario

The foreshock region of a CME shock front, where shock accelerated electrons form a beam population in the otherwise quiescent plasma is generally assumed to be the source region of type II radio bursts. Nonlinear wave interaction of electrostatic waves excited by the beamed electrons are the prime candidates for the radio waves’ emission.To address the question whether a single, or two counterpropagating beam populations are a requirement for this process, we have conducted 2.5D particle-in-cell simulations using the fully relativistic ACRONYM code.Results show indications of three-wave interaction leading to electromagnetic emission at the fundamental and harmonic frequency for the two-beam case. For the single-beam case, no such signatures were detectable.

Particle scattering in turbulent plasmas with amplified wave modes

High-energy particles stream during coronal mass ejections or flares through the plasma of the solar wind. This causes instabilities, which lead to wave growth at specific resonant wave numbers, especially within shock regions. These amplified wave modes influence the turbulent scattering process significantly. In this paper, results of particle transport and scattering in turbulent plasmas with excited wave modes are presented. The method used is a hybrid simulation code, which treats the heliospheric turbulence by an incompressible magnetohydrodynamic approach separately from a kinetic particle description. Furthermore, a semi-analytical model using quasilinear theory (QLT) is compared to the numerical results. This paper aims at a more fundamental understanding and interpretation of the pitch-angle scattering coefficients. Our calculations show a good agreement of particle simulations and the QLT for broad-band turbulent spectra; for higher turbulence levels and particle beam driven plasmas, the QLT approximation gets worse. Especially the resonance gap at μ = 0 poses a well-known problem for QLT for steep turbulence spectra, whereas test-particle computations show no problems for the particles to scatter across this region. The reason is that the sharp resonant wave-particle interactions in QLT are an oversimplification of the broader resonances in test-particle calculations, which result from nonlinear effects not included in the QLT. We emphasise the importance of these results for both numerical simulations and analytical particle transport approaches, especially the validity of the QLT. n Appendices A-D are available in electronic form at http://www.aanda.org

Nonlinear Wave Interactions as Emission Process of Type II Radio Bursts

The emission of fundamental and harmonic frequency radio waves of type II radio bursts are assumed to be products of three-wave interaction processes of beam-excited Langmuir waves. Using a particle-in-cell code, we have performed simulations of the assumed emission region, a coronal mass ejection foreshock with two counterstreaming electron beams. Analysis of wavemodes within the simulation shows self-consistent excitation of beam-driven modes, which yield interaction products at both fundamental and harmonic emission frequencies. Through variation of the beam strength, we have investigated the dependence of energy transfer into electrostatic and electromagnetic modes, confirming the quadratic dependence of electromagnetic emission on electron beam strength.

The Influence of the Mass Ratio on Particle Acceleration by the Filamentation Instability

Observations indicate that several types of astrophysical sources produce relativistic jets that interact with the intergalactic medium, creating regions of counterstreaming plasma. Under these conditions the plasma is susceptible to filamentation instabilities. Analytical analysis of this environment is highly non-trivial, which leads to the extensive use of computer simulations to study these conditions and the connection to the energetic photons and particles emanating from these sources. To make simulations feasible one has to make a couple of simplifications to reduce the computational complexity to a level that is reachable with todays computers. One such simplification is the reduction of the proton mass compared to the electron mass. This project tries to assess what the lower limit of this quantity is that still allows a realistic representation of the situation in nature.

Evolution of plasma turbulence excited with particle beams

Particles ejected from the Sun that stream through the surrounding plasma of the solar wind are causing instabilities. These generate wavemodes in a certain frequency range especially within shock regions, where particles are accelerated. The aim of this paper is to investigate of amplified Alfvenic wavemodes in driven incompressible magnetohydrodynamic turbulence. Results of different heliospheric scenarios from isotropic and anisotropic plasmas, as well as turbulence near the critical balance are shown. The energy transport of the amplified wavemode is governed by the mechanisms of diffusion, convection and dissipation of energy in wavenumber space. The strength of these effects varies with energy and wavenumber of the mode in question. Two-dimensional energy spectra of spherical k-space integration that permit detailed insight into the k� /k⊥-development are presented. The evolution of energy injected through driving shows a strong energy transfer to perpendicular wavemodes. The main process ∂ ˜

Multiwavelength periodicity study of Markarian 501

Context. Active galactic nuclei (AGN) are highly variable emitters of electromagnetic waves from the radio to the gamma-ray regime. This variability may be periodic, which in turn could be the signature of a binary black hole. Systems of black holes are strong emitters of gravitational waves whose amplitude depends on the binary orbital parameters such as the component mass, the orbital semi-major-axis and eccentricity. Aims. It is our aim to prove the existence of periodicity of the AGN Markarian 501 from several observations in different wavelengths. A simultaneous periodicity in different wavelengths provides evidence of bound binary black holes in the core of AGN. Methods. Existing data sets from observations by Whipple, SWIFT, RXTE, and MAGIC have been analysed with the Lomb-Scargle method, the epoch-folding technique and the SigSpec software. Results. Our analysis shows a 72-day period, which could not be seen in previous works due to the limited length of observations. This does not contradict a 23-day period that can be derived as a higher harmonic from the 72-day period.

Energy loss in intergalactic pair beams: Particle-in-cell simulation

Aims. The change in the distribution function of electron-positron pair beams determines whether GeV photons can be produced as secondary radiation from TeV photons. We will discuss the instabilities driven by pair beams. Methods. The system of a thermal proton-electron plasma and the electron-positron beam is collision free. We have, therefore, used the particle-in-cell simulation approach. It was necessary to alter the physical parameters, but the ordering of growth rates has been retained. Results. We were able to show that plasma instabilities can be recovered in particle-in-cell simulations, but their e ect on the pair distribution function is negligible for the beam-background energy density ratios typically found in blazars.