Cosmic Rays and Stochastic Magnetic Reconnection in the Heliotail

Abstract

Galactic cosmic rays are believed to be generated by diffusive shock acceleration processes in Supernova Remnants, and the arrival direction is likely determined by the distribution of their sources throughout the Galaxy, in particular by the nearest and youngest ones. Transport to Earth through the interstellar medium is expected to affect the cosmic ray properties as well. However, the observed anisotropy of TeV cosmic rays and its energy dependence cannot be explained with diffusion models of particle propagation in the Galaxy. Within a distance of a few parsec, diffusion regime is not valid and particles with energy below about 100 TeV must be influenced by the heliosphere and its elongated tail. The observation of a highly significant localized excess region of cosmic rays from the apparent direction of the downstream interstellar flow at 1-10 TeV energies might provide the first experimental evidence that the heliotail can affect the transport of energetic particles. In particular, TeV cosmic rays propagating through the heliotail interact with the 100-300 AU wide magnetic field polarity domains generated by the 11 year cycles. Since the strength of non-linear convective processes is expected to be larger than viscous damping, the plasma in the heliotail is turbulent. Where magnetic field domains converge on each other due to solar wind gradient, stochastic magnetic reconnection likely occurs. Such processes may be efficient enough to re-accelerate a fraction of TeV particles as long as scattering processes are not strong. Therefore the fractional excess of TeV cosmic rays from the narrow region toward the heliotail direction traces sightlines with the lowest smearing scattering effects, that can also explain the observation of a harder than average energy spectrum.

14 pages, 7 figures. Accepted for publication by Nonlinear Processes in Geophysics

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• Anisotropy in Cosmic-Ray Arrival Directions in the Southern Hemisphere with Six Years of Data from the IceCube Detector
• Anisotropy of TeV Cosmic Rays and the Outer Heliospheric Boundaries
• Neutrinos and Cosmic Rays Observed by IceCube
• Cosmic Ray Small Scale Anisotropies and Local Turbulent Magnetic Fields
• 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
• Observation of TeV-PeV cosmic ray anisotropy with IceCube, IceTop and AMANDA
• Snowmass 2021 LoI: Determination of cosmic ray properties in the local interstellar medium with all-sky anisotropy observations
• Experimental biases on the heliospheric contribution to the observed TeV cosmic ray anisotropy