Large-Scale Cosmic-Ray Anisotropy as a Probe of Interstellar Turbulence

Abstract

We calculate the large-scale cosmic-ray (CR) anisotropies predicted for a range of Goldreich-Sridhar (GS) and isotropic models of interstellar turbulence, and compare them with IceTop data. In general, the predicted CR anisotropy is not a pure dipole; the cold spots reported at 400 TeV and 2 PeV are consistent with a GS model that contains a smooth deficit of parallel-propagating waves and a broad resonance function, though some other possibilities cannot, as yet, be ruled out. In particular, isotropic fast magnetosonic wave turbulence can match the observations at high energy, but cannot accommodate an energy dependence in the shape of the CR anisotropy. Our findings suggest that improved data on the large-scale CR anisotropy could provide a valuable probe of the properties - notably the power-spectrum - of the interstellar turbulence within a few tens of parsecs from Earth.

20 pages, 12 figures. Published in The Astrophysical Journal

References in corpus (6)

• The outer scale of turbulence in the magneto-ionized Galactic interstellar medium
• Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field
• Observation of Cosmic Ray Anisotropy with the IceTop Air Shower Array
• Solution to the cosmic ray anisotropy problem
• Probing Nearby CR Accelerators and ISM Turbulence with Milagro Hot Spots
• Magnetic fields and cosmic ray anisotropies at TeV energies

Cited by in corpus (4)

• All-Sky Measurement of the Anisotropy of Cosmic Rays at 10 TeV and Mapping of the Local Interstellar Magnetic Field
• 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
• Diffusion of relativistic charged particles and field lines in isotropic turbulence: I. Numerical simulations