R. Engel

BL Lac objects in the synchrotron proton blazar model

We calculate the spectral energy distribution (SED) of electromagnetic radiation and the spectrum of high-energy neutrinos from BL Lac objects in the context of the synchrotron proton blazar model. In this model, the high-energy hump of the SED is due to accelerated protons, while most of the low-energy hump is due to synchrotron radiation by co-accelerated electrons. To accelerate protons to sufficiently high energies to produce the high-energy hump, rather high magnetic fields are required. Assuming reasonable emission region volumes and Doppler factors, we then find that in low-frequency peaked BL Lacs (LBLs), which have higher luminosities than high-frequency peaked BL Lacs (HBLs), there is a significant contribution to the high-frequency hump of the SED from pion photoproduction and subsequent cascading, including synchrotron radiation by muons. In contrast, in HBLs we find that the high-frequency hump of the SED is dominated by proton synchrotron radiation. We are able to model the SED of typical LBLs and HBLs, and to model the famous 1997 flare of Markarian 501. We also calculate the expected neutrino output of typical BL Lac objects, and estimate the diffuse neutrino intensity due to all BL Lacs. Because pion photoproduction is inefficient in HBLs, as protons lose energy predominantly by synchrotron radiation, the contribution of LBLs dominates the diffuse neutrino intensity. We suggest that nearby LBLs may well be observable with future high-sensitivity TeV γ-ray telescopes.

Neutrinos from propagation of ultrahigh-energy protons

We present a calculation of the production of neutrinos during propagation of ultra-high energy cosmic rays from their astrophysical sources to us. Photoproduction interactions are modeled with the event generator SOPHIA that represents very well the experimentally measured particle production cross sections at accelerator energies. We give the fluxes expected from different assumptions on cosmic ray source distributions, cosmic ray injection spectra, cosmological evolution of the sources and different cosmologies, and compare them to the Waxman-Bahcall limit on source neutrinos. We estimate rates for detection of neutrino induced showers in a km3 water detector. The ratio of the local high energy neutrino flux to the ultra-high energy cosmic ray flux is a crucial parameter in distinguishing between astrophysical and cosmological (top-down) scenarios of the ultra-high energy cosmic ray origin.

Monte Carlo simulations of photohadronic processes in astrophysics

Abstract A new Monte Carlo program for photohadronic interactions of relativistic nucleons with an ambient photon radiation field is presented. The event generator is designed to fulfill typical astrophysical requirements, but can also be used for radiation and background studies at high energy colliders such as LEP2 and HERA, as well as for simulations of photon induced air showers. We consider the full photopion production cross section from the pion production threshold up to high energies. It includes resonance excitation and decay, direct single pion production and diffractive and non-diffractive multiparticle production. The cross section of each individual process is calculated by fitting experimental data, while the kinematics is determined by the underlying particle production process. We demonstrate that our model is capable of reproducing known accelerator data over a wide energy range.

The Monte Carlo Event Generator DPMJET-III

A new version of the Monte Carlo event generator Dpmjet is presented. It is a code system based on the Dual Parton Model and unifies all features of the Dtunuc-2, Dpmjet-II and Phojet1.12 event generators. Dpmjet-III allows the sim- ulation of hadron-hadron, hadron-nucleus, nucleus-nucleus, photon-hadron, photon- photon and photon-nucleus interactions from a few GeV up to the highest cosmic ray energies. Hadronic collisions at high energies involve the production of particles with low transverse momenta, the so-called soft multiparticle production. The theoretical tools available at present are not sufficient to understand this feature from QCD and phenomenological models are typically applied instead. The Dual Parton Model (DPM) (1) is such a model and its fundamental ideas are presently the basis of many of the Monte Carlo (MC) implementations of soft interactions in codes used for Radiation Physics simulations. Many of these implementations are however limited in their application by, for example, the collision energy range which they are able to describe or by the collision partners (hadrons, nuclei, photons) which the model can be used for. With respect to modern multi-purpose codes for particle interaction and transport these limitations at high energy are clearly often a disadvantage. In this paper we present the Dpmjet-III code system, a MC event generator based on the DPM which is unique in its wide range of application. Dpmjet-III is capable of simulating hadron-hadron, hadron-nucleus, nucleus-nucleus, photon- hadron, photon-photon and photon-nucleus interactions from a few GeV up to the highest cosmic ray energies. In the present paper we give an overview over the different components and models of Dpmjet-III and present a few examples for comparisons of model results with experimental data.

Propagation of ultrahigh energy protons in the nearby universe

We present a new calculation of the propagation of protons with energies above 10{sup 19} eV over distances of up to several hundred Mpc. The calculation is based on a Monte Carlo approach using the event generator SOPHIA for the simulation of hadronic nucleon-photon interactions and a realistic integration of the particle trajectories in a random extragalactic magnetic field. Accounting for the proton scattering in the magnetic field affects noticeably the nucleon energy as a function of the distance to their source and allows us to give realistic predictions on arrival energy, time delay, and arrival angle distributions and correlations as well as secondary particle production spectra.

Antiprotons at Solar Maximum

New measurements with good statistics will make it possible to observe the time variation of cosmic antiprotons at 1 AU through the approaching peak of solar activity. We report a new computation of the interstellar antiproton spectrum expected from collisions between cosmic protons and the interstellar gas. This spectrum is then used as input to a steady-state drift model of solar modulation, in order to provide predictions for the antiproton spectrum as well as the antiproton/proton ratio at 1 AU. Our model predicts a surprisingly large, rapid increase in the antiproton/proton ratio through the next solar maximum, followed by a large excursion in the ratio during the following decade.

Universality of electron distributions in high-energy air showers—Description of Cherenkov light production

Abstract The shower simulation code CORSIKA has been used to investigate the electron energy and angular distributions in high-energy showers. Based on the universality of both distributions, we develop an analytical description of Cherenkov light emission in extensive air showers, which provides the total number and angular distribution of photons. The parameterisation can be used e.g. to calculate the contribution of direct and scattered Cherenkov light to shower profiles measured with the air fluorescence technique.

Reconstruction of Longitudinal Profiles of Ultra-High Energy Cosmic Ray Showers from Fluorescence and Cherenkov Light Measurements

We present a new method for the reconstruction of the longitudinal profile of extensive air showers induced by ultra-high energy cosmic rays. In contrast to the typically considered shower size profile, this method employs directly the ionization energy deposit of the shower particles in the atmosphere. Due to universality of the energy spectra of electrons and positrons, both fluorescence and Cherenkov light can be used simultaneously as signal to infer the shower profile from the detected light. The method is based on an analytic least-square solution for the estimation of the shower profile from the observed light signal. Furthermore, the extrapolation of the observed part of the profile with a Gaisser–Hillas function is discussed and the total statistical uncertainty of shower parameters like total energy and shower maximum is calculated.

Ultrahigh-Energy Cosmic-Ray Propagation in the Galaxy: Clustering versus Isotropy

Recently, the Akeno Giant Air Shower Array Collaboration presented data suggesting a significant clustering of ultrahigh-energy cosmic rays coming from the outer Galaxy region. In this paper we calculate expected cosmic-ray arrival distributions for several simple source location scenarios that bracket the more realistic ones and investigate the possibility of clustering and correlation effects. The role of the Galactic magnetic field is discussed in detail.

Hybrid simulations of extensive air showers

We present a fast one dimensional hybrid method to efficiently simulate extensive air showers up to the highest observed energies. Based on precalculated pion showers and a bootstrap technique, our method predicts the average shower profile, the number of muons at detector level above several energy thresholds as well as the fluctuations of the electromagnetic and hadronic components of the shower. We study the main characteristics of proton-induced air showers up to ultra high energy, comparing the predictions of three different hadronic interaction models: SIBYLL 1.7, SIBYLL 2.1 and QGSJET98. The influence of the hadronic interaction models on the shower evolution, in particular the elongation rate, is discussed and the applicability of analytical approximations is investigated.