The Original Anisotropy of TeV Cosmic Rays in the Local Interstellar Medium

Abstract

Abstract This paper presents the original anisotropy that TeV cosmic rays (CRs) have in the local interstellar medium. This anisotropy is obtained using a method of flux mapping with the Liouville theorem and a magnetohydrodynamic (MHD) heliosphere model of the electromagnetic field to remove the particle propagation effects hidden in the measurements made by the Tibet ASγ experiment at Earth. The original interstellar anisotropy turns out to be almost a pure dipole, which results from a diffusion flow of CRs escaping along the local interstellar magnetic field into the northern Galactic halo. The observed anisotropy maps at Earth appear quite complex because the heliosphere distorts the dipole anisotropy, generating a significant amount of high-order multipoles, while interstellar magnetic field fluctuations contribute to some weak anisotropy on small angular scales. It is found that the density gradient of these CRs points approximately toward Vela in the Local Bubble, providing experimental evidence to show that the local supernova is making a special contribution to the TeV CRs we see at Earth. This special contribution will keep growing in the future tens of thousand years. The original anisotropy also reveals that the CRs spread from the source primarily along the interstellar magnetic field, while experiencing a nearly isotropic pitch-angle scattering process caused by interstellar turbulence.