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The landscape of high- and ultra-high-energy astrophysics has changed in the last decade, largely due to the inflow of data collected by large-scale cosmic-ray, gamma-ray, and neutrino observatories. At the dawn of the multimessenger era, the interpretation of these observations within a consistent framework is important to elucidate the open questions in this field. CRPropa 3.2 is a Monte Carlo code for simulating the propagation of high-energy particles in the Universe. This version represents a major leap forward, significantly expanding the simulation framework and opening up the possibility for many more astrophysical applications. This includes, among others: efficient simulation of high-energy particles in diffusion-dominated domains, self-consistent and fast modelling of electromagnetic cascades with an extended set of channels for photon production, and studies of cosmic-ray diffusion tensors based on updated coherent and turbulent magnetic-field models. Furthermore, several technical updates and improvements are introduced with the new version, such as: enhanced interpolation, targeted emission of sources, and a new propagation algorithm (Boris push). The detailed description of all novel features is accompanied by a discussion and a selected number of example applications., Comment: 32 pages, 9 figures

Many attempts have been made to provide catalogs of potential sources of ultra-high energy cosmic ray (UHECR) particles based on various astronomical tracers, such as observed radio or gamma-ray emission. A closer look reveals, however, that they all suffer from significant bias and selection effects. We present here a demo-version of a catalog for one often-discussed UHECR source class, radio galaxies (or radio-loud AGN), which is based on a complete theoretical description of jet-energetics, particle acceleration physics, relativistic beaming effects and nuclear composition, parametrized by a comprehensible set of adjustable physical quantities. In addition to the bright radio galaxies Centaurus A, Virgo A, Fornax A and Cygnus A discussed in previous work, we find several sources with blazar-like properties that can contribute on a similar level if relativistic beaming effects are considered. We present a simple method to test the basic properties of the catalog for any choice of parameters (without the need to run expensive simulations), and find that in the canonical case the anisotropy signals expected from radio galaxies promise to be in good agreement with current observational findings. In particular, radio galaxies can reproduce almost exactly the direction of the dipole above 8 EeV detected by the Pierre Auger Observatory if we assume that extragalactic magnetic fields are strong (>1nG) only in structures, but very weak in voids. We plan to provide a completed and improved version of this catalog in electronic form, to be used in more detailed UHECR propagation simulations. For immediate applications, we suggest a complete set of 16 strong UHECR sources which can contribute to UHECR anisotropy on the level which can be currently probed by experiment, and note that 6 of them have not been considered in any previous studies., Comment: 8 pages, 2 figures, paper presented at the 36th International Cosmic Ray Conference (ICRC2019), July 24th - August 1st, Madison, WI, USA; updated and final version

The propagation of charged cosmic rays through the Galactic environment influences all aspects of the observation at Earth. Energy spectrum, composition and arrival directions are changed due to deflections in magnetic fields and interactions with the interstellar medium. Today the transport is simulated with different simulation methods either based on the solution of a transport equation (multi-particle picture) or a solution of an equation of motion (single-particle picture). We developed a new module for the publicly available propagation software CRPropa 3.1, where we implemented an algorithm to solve the transport equation using stochastic differential equations. This technique allows us to use a diffusion tensor which is anisotropic with respect to an arbitrary magnetic background field. The source code of CRPropa is written in C++ with python steering via SWIG which makes it easy to use and computationally fast. In this paper, we present the new low-energy propagation code together with validation procedures that are developed to proof the accuracy of the new implementation. Furthermore, we show first examples of the cosmic ray density evolution, which depends strongly on the ratio of the parallel $\kappa_\parallel$ and perpendicular $\kappa_\perp$ diffusion coefficients. This dependency is systematically examined as well the influence of the particle rigidity on the diffusion process., Comment: Accepted for publication in JCAP, 33 pages, 17 figures

The origin of cosmic rays is one of the long-standing mysteries in physics and astrophysics. Simple arguments suggest that a scenario of supernova remnants (SNRs) in the Milky Way as the dominant sources for the cosmic ray population below the knee could work: in a generic calculation, it can be shown that these objects can provide the energy budget necessary to explain the observed flux of cosmic rays. However, this argument is based on the assumption that all sources behave in the same way, i.e.\ they all have the same energy budget, spectral behavior and maximum energy. In this paper, we investigate if a realistic population of SNRs is capable of producing the cosmic ray flux as it is observed below the knee. We use 21 SNRs that are well-studied from radio wavelengths up to gamma-ray energies. It could be shown previously (Mandelartz & Becker Tjus 2015) that the high-energy bump in the energy spectrum of these 21 sources can be dominated by hadronic emission. Here, gamma-rays are produced via $\pi^{0}-$decays from cosmic ray interactions in molecular clouds near the supernova remnant, which serves as the cosmic ray accelerator. The cosmic ray spectra show a large variety in their energy budget, spectral behavior and maximum energy. These sources are assumed to be representative for the total class of SNRs, where we assume that about 100 - 200 cosmic ray emitting SNRs should be present today. Finally, we use these source spectra to simulate the cosmic ray transport from individual SNRs in the Galaxy with the GALPROP code for cosmic ray propagation. We find that the cosmic ray budget can be matched well for a diffusion coefficient that is close to $D\propto E^{0.3}$. A stronger dependence on the energy, e.g. $E^{0.5}$, would lead to a spectrum at Earth that is too steep when compared to what is detected and the energy budget cannot be matched, in particular toward high energies., Comment: 43 pages, 7 figures

We present a systematic study of the non-thermal electron-proton plasma and its emission processes in starburst galaxies in order to explain the correlation between the luminosity in the radio band and the recently observed gamma luminosity. In doing so, a steady state description of the cosmic ray electrons and protons within the spatially homogeneous starburst is considered where continuous momentum losses are included as well as catastrophic losses due to diffusion and advection. The primary source of the relativistic cosmic rays, e.g. supernova remnants, provides a quasi-neutral plasma with a power law spectrum in momentum where we account for rigidity dependent differences between the electron and proton spectrum. We examine the resulting leptonic and hadronic radiation processes by synchrotron radiation, inverse Compton scattering, Bremsstrahlung and hadronic pion production. Finally, the observations of NGC 253, M82, NGC 4945 and NGC 1068 in the radio and gamma-ray band as well as the observed supernova rate are used to constrain a best-fit model. In the case of NGC 253, M82, NGC 4945 our model is able to accurately describe the data, showing that: (i) Supernovae are the dominant particle accelerators for NGC 253, M82 and NGC 4945, but not in the case of NGC 1068. (ii) All considered starburst galaxies are poor proton calorimeters in which for NGC 253 the escape is predominantly driven by the galactic wind, whereas the diffusive escape dominates in NGC 4945 and M82 (at energies > 1TeV). (iii) Secondary electrons from hadronic pion production are important to model the radio flux, but the associated neutrino flux is below the current observation limit.