Cosmic Ray Small Scale Anisotropies and Local Turbulent Magnetic Fields

Abstract

Cosmic ray anisotropy has been observed in a wide energy range and at different angular scales by a variety of experiments over the past decade. However, no comprehensive or satisfactory explanation has been put forth to date. The arrival distribution of cosmic rays at Earth is the convolution of the distribution of their sources and of the effects of geometry and properties of the magnetic field through which particles propagate. It is generally believed that the anisotropy topology at the largest angular scale is adiabatically shaped by diffusion in the structured interstellar magnetic field. On the contrary, the medium- and small-scale angular structure could be an effect of non-diffusive propagation of cosmic rays in perturbed magnetic fields. In particular, a possible explanation of the observed small-scale anisotropy observed at TeV energy scale, may come from the effect of particle scattering in turbulent magnetized plasmas. We perform numerical integration of test particle trajectories in low-$\beta$ compressible magnetohydrodynamic turbulence to study how the cosmic rays arrival direction distribution is perturbed when they stream along the local turbulent magnetic field. We utilize Liouville's theorem for obtaining the anisotropy at Earth and provide the theoretical framework for the application of the theorem in the specific case of cosmic ray arrival distribution. In this work, we discuss the effects on the anisotropy arising from propagation in this inhomogeneous and turbulent interstellar magnetic field.

14 pages, 7 figures. Accepted for publication in ApJ

References in corpus (14)

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Cited by in corpus (20)

• The origin of Galactic cosmic rays: challenges to the standard paradigm
• Origin of Small-Scale Anisotropies in Galactic Cosmic Rays
• Diffusion of cosmic rays in MHD turbulence with magnetic mirrors
• All-Sky Measurement of the Anisotropy of Cosmic Rays at 10 TeV and Mapping of the Local Interstellar Magnetic Field
• Test particle simulations of cosmic rays
• Neutrinos and Cosmic Rays Observed by IceCube
• Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory
• Large-Scale Cosmic-Ray Anisotropy as a Probe of Interstellar Turbulence
• TeV Cosmic-Ray Anisotropy from the Magnetic Field at the Heliospheric Boundary
• Measurements and implications of cosmic ray anisotropies from TeV to trans-EeV energies
• Cosmic rays and random magnetic traps
• No longer ballistic, not yet diffusive--the formation of cosmic ray small-scale anisotropies
• Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with 12 yr of Data Collected by the IceCube Neutrino Observatory
• Comic ray flux anisotropies caused by astrospheres
• Time variability of TeV cosmic ray sky map
• Revisiting the implications of Liouville's theorem to the anisotropy of cosmic rays
• Diffusion of relativistic charged particles and field lines in isotropic turbulence: I. Numerical simulations
• Cosmic Ray transport in mixed magnetic fields and their role on the observed anisotropies
• Chaotic Behavior of Trapped Cosmic Rays
• The Dipole Anisotropy of Galactic Cosmic Rays