The cosmic-ray Sun shadow, which is caused by high-energy charged cosmic rays being blocked and deflected by the Sun and its magnetic field, has been observed by various experiments, such as ...Argo-YBJ, Tibet, HAWC, and IceCube. Most notably, the shadow’s size and depth was recently shown to correlate with the 11-year solar cycle. The interpretation of such measurements, which help to bridge the gap between solar physics and high-energy particle astrophysics, requires a solid theoretical understanding of cosmic-ray propagation in the coronal magnetic field. It is the aim of this paper to establish theoretical predictions for the cosmic-ray Sun shadow in order to identify observables that can be used to study this link in more detail. To determine the cosmic-ray Sun shadow, we numerically compute trajectories of charged cosmic rays in the energy range of 5−316 TeV for five different mass numbers. We present and analyze the resulting shadow images for protons and iron, as well as for typically measured cosmic-ray compositions. We confirm the observationally established correlation between the magnitude of the shadowing effect and both the mean sunspot number and the polarity of the magnetic field during the solar cycle. We also show that during low solar activity, the Sun’s shadow behaves similarly to that of a dipole, for which we find a non-monotonous dependence on energy. In particular, the shadow can become significantly more pronounced than the geometrical disk expected for a totally unmagnetized Sun. For times of high solar activity, we instead predict the shadow to depend monotonously on energy and to be generally weaker than the geometrical shadow for all tested energies. These effects should become visible in energy-resolved measurements of the Sun shadow, and may in the future become an independent measure for the level of disorder in the solar magnetic field.
The recent observations of muon charge ratio up to about 10 TeV and of atmospheric neutrinos up to energies of about 400 TeV has triggered a renewed interest into the high-energy interaction models ...and cosmic ray primary composition. A reviewed calculation of lepton spectra produced in cosmic ray induced extensive air showers is carried out with a primary cosmic ray spectrum that fits the latest direct measurements below the knee. In order to achieve this, we used a full Monte Carlo method to derive the inclusive differential spectra (yields) of muons, muon neutrinos and electron neutrinos at the surface for energies between 80 GeV and hundreds of PeV. Using these results the differential flux and the flavor ratios of leptons were calculated. Furthermore, we could quantify systematic uncertainties of atmospheric muon- and neutrino fluxes, associated to the models of the primary cosmic ray spectrum and the interaction models.
Context. Over the past few years, signatures of supernova remnants have been detected in gamma rays, particularly those that are known to be associated with molecular clouds. Whether these gamma rays ...are generated by cosmic-ray electrons emitting bremsstrahlung or experiencing inverse Compton scattering, or by cosmic-ray protons interacting with ambient hydrogen is usually not known. The detection of hadronic ionization signatures in spatial coincidence with gamma-ray signatures can help to unambiguously identify supernova remnants as sources of cosmic-ray protons. Aims. Our central aim is to develop a method to investigate whether the gamma rays are formed by cosmic-ray protons. To achieve this goal, we derived the position-dependent cosmic-ray-induced and photoinduced ionization rates. Methods. To calculate hadronic signatures from cosmic-ray-induced ionization to examine the origin of the observed gamma rays from molecular clouds associated with supernova remnants, we solved analytically the transport equation for cosmic-ray protons propagating in a molecular cloud, including the relevant momentum-loss processes, and determined the proton flux at any penetration depth into the cloud. Results. Because the solution of the transport equation is obtained for arbitrary source functions, it can be used for a variety of supernova remnants. We derived the corresponding theoretical ionization rate as a function of the penetration depth from the position-dependent proton flux, and compared it with photoinduced ionization profiles for available X-ray data in a case study with four supernova remnants associated with molecular clouds. Three of the remnants show a clear dominance of the hadronically induced ionization rate, while for one remnant, X-ray emission seems to dominate by a factor of 10. Conclusions. This is the first derivation of position-dependent profiles for cosmic-ray-induced ionization with an analytic solution for arbitrary cosmic-ray source spectra. The cosmic-ray-induced ionization has to be compared with photoionization for strong X-ray sources. For this purpose, measurements of X-ray spectra from supernova remnant shocks in the sub-keV to keV domain are necessary for a proper comparison. For sources dominated by cosmic-ray-induced ionization (e.g., W49B), the ionization profiles can be used in the future to map the spatial structure of hadronic gamma rays and rotation-vibrational lines induced by cosmic-ray protons. With instruments such as ALMA for the line signatures and CTA for the gamma-ray detection, this correlation study will help to identify sources of hadronic cosmic rays.
Active galactic nuclei (AGN) are believed to be the source of ultra high energy cosmic rays (UHECRs, E>1018eV). Particles are assumed to be accelerated in the accretion disk and the plasma jets, ...produced due to conservation of angular momentum, to the highest energies, where they interact with each other and produce pions, which decay among others in neutrinos.
For a known cosmic ray (CR) spectral behavior, the main parameters in the calculation of the neutrino flux from proton–proton (p–p) interactions are the target density nH and the ratio of electrons to protons fe. Using most recent neutrino flux limits from IceCube point source searches, we set limits on the target densities for 33 FR-I galaxies. The densities are shown to be smaller than 30cm-3 to 2·103cm-3, depending on the source and when using a fixed electron to proton ratio of fe=0.1. This implies that some CR acceleration sites, especially those close to the core of the AGN, can already be excluded, or else that the ratio of electrons to protons deviates significantly from the commonly used value of 0.1.
For Centaurus A (Cen A) and Messier 87 (M 87) we use Fermi observations to model the γ-flux, the neutrino flux and the resulting target density. The detection of these neutrinos will help to find information about acceleration processes in the source.
The statistics of black holes and their masses strongly suggests that their mass distribution has a cut-off towards lower masses near 3 × 106 M⊙. This is consistent with a classical formation ...mechanism from the agglomeration of the first massive stars in the universe. However, when the masses of the stars approach 106 M⊙, the stars become unstable and collapse, possibly forming the first generation of cosmological black holes. Here, we speculate that the claimed detection of an isotropic radio background may constitute evidence of the formation of these first supermassive black holes, since their data are compatible in spectrum and intensity with synchrotron emission from the remnants. The model proposed fulfils all observational conditions for the background, in terms of single-source strength, number of sources, far-infrared and gamma-ray emission. The observed high-energy neutrino flux is consistent with our calculations in flux and spectrum. The proposal described in this paper may also explain the early formation and growth of massive bulge-less disc galaxies as derived from the massive, gaseous shell formed during the explosion prior to the formation of a supermassive black hole.
Motivated by cosmic ray (CR) re-acceleration at a potential Galactic Wind Termination Shock (GWTS), we present a numerical model for time-dependent Diffusive Shock Acceleration (DSA). We use the ...stochastic differential equation solver (DiffusionSDE) of the cosmic ray propagation framework CRPropa3.2 with two modifications: An importance sampling module is introduced to improve statistics at high energies in order to keep the simulation time short. An adaptive time step is implemented in the DiffusionSDE module. This ensures to efficiently meet constraints on the time and diffusion step, which is crucial to obtain the correct shock spectra. The time evolution of the spectrum at a one-dimensional planar shock is verified against the solution obtained by the grid-based solver VLUGR3 for both energy-independent and energy-dependent diffusion. We show that the injection of pre-accelerated particles can lead to a broken power law spectrum in momentum if the incoming spectrum of CRs is harder than the re-accelerated spectrum. If the injected spectrum is steeper, the shock spectrum dominates at all energies. We finally apply the developed model to the GWTS by considering a spherically symmetric shock, a spiral Galactic magnetic field, and anisotropic diffusion. The time-dependent spectrum at the shock is modeled as a basis for further studies.
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