Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. II: anisotropy

We investigate the effects of stochasticity in the spatial and temporal distribution of supernova remnants on the anisotropy of cosmic rays observed at Earth. The calculations are carried out for different choices of the diffusion coefficient D(E) for propagation in the Galaxy. The propagation and spallation of nuclei are taken into account. At high energies we assume that $D(E)\sim(E/Z)^{\delta}$, with $\delta=1/3$ and $\delta=0.6$ being the reference scenarios. The large scale distribution of supernova remnants in the Galaxy is modeled following the distribution of pulsars with and without accounting for the spiral structure of the Galaxy. Our calculations allow us to determine the contribution to anisotropy resulting from both the large scale distribution of SNRs in the Galaxy and the random distribution of the nearest remnants. The naive expectation that the anisotropy amplitude scales as D(E) is shown to be an oversimplification which does not reflect in the predicted anisotropy for any realistic distribution of the sources. The fluctuations in the anisotropy pattern are dominated by nearby sources, so that predicting or explaining the observed anisotropy amplitude and phase becomes close to impossible. We find however that the very weak energy dependence of the anisotropy amplitude below $10^{5}$ GeV and the rise at higher energies, can best be explained if the diffusion coefficient is $D(E)\sim E^{1/3}$. Faster diffusion, for instance with $\delta=0.6$, leads in general to an exceedingly large anisotropy amplitude. The spiral structure introduces interesting trends in the energy dependence of the anisotropy pattern, which qualitatively reflect the trend seen in the data. For large values of the halo size we find that the anisotropy becomes dominated by the large scale regular structure of the source distribution, leading indeed to a monotonic increase of $\delta_A$ with energy.Comment: 21 Pages, to appear in JCA

Effects of the galactic magnetic field upon large scale anisotropies of extragalactic Cosmic Rays

The large scale pattern in the arrival directions of extragalactic cosmic rays that reach the Earth is different from that of the flux arriving to the halo of the Galaxy as a result of the propagation through the galactic magnetic field. Two different effects are relevant in this process: deflections of trajectories and (de)acceleration by the electric field component due to the galactic rotation. The deflection of the cosmic ray trajectories makes the flux intensity arriving to the halo from some direction to appear reaching the Earth from another direction. This applies to any intrinsic anisotropy in the extragalactic distribution or, even in the absence of intrinsic anisotropies, to the dipolar Compton-Getting anisotropy induced when the observer is moving with respect to the cosmic rays rest frame. For an observer moving with the solar system, cosmic rays traveling through far away regions of the Galaxy also experience an electric force coming from the relative motion (due to the rotation of the Galaxy) of the local system in which the field can be considered as being purely magnetic. This produces small changes in the particles momentum that can originate large scale anisotropies even for an isotropic extragalactic flux.Comment: 11 pages, 4 figure

Rigidity dependent knee and cosmic ray induced high energy neutrino fluxes

Scenarios in which the knee of the cosmic ray spectrum depends on the particle rigidities usually predict that the cosmic ray composition becomes heavier above the knee and have associated a change in the spectral slope of each individual nuclear component which is steeper than the change ($\Delta\alpha\simeq 0.3$) observed in the total spectrum. We show that this implies that the very high energy ($E_\nu>10^{14}$ eV) diffuse neutrino fluxes produced by cosmic rays hitting the atmosphere or colliding with the interstellar medium in the Galaxy will be significantly suppressed, making their detection harder but also reducing the background for the search of other (more challenging) astrophysical neutrino sources.Comment: 20 pages, 5 figure

Study of UHE cosmic neutrinos through horizontal extensive air showers

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Istituto Nazionale di Fisica Nucleare, Via E. Fermi, 40 -Frascati - Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Study of UHE cosmic neutrinos through horizontal extensive air showers

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome; Istituto Nazionale di Fisica Nucleare, Via E. Fermi, 40 Frascati / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Study of jet production in p-N interactions at square roots approx 500 GeV in EAS multicore events

Physics Letters B (in press)Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal