Northern sky Galactic Cosmic Ray anisotropy between 10-1000 TeV with the Tibet Air Shower Array

Abstract

We report the analysis of the $10-1000$ TeV large-scale sidereal anisotropy of Galactic cosmic rays (GCRs) with the data collected by the Tibet Air Shower Array from October, 1995 to February, 2010. In this analysis, we improve the energy estimate and extend the declination range down to $-30^{\circ}$. We find that the anisotropy maps above 100 TeV are distinct from that at multi-TeV band. The so-called "tail-in" and "loss-cone" features identified at low energies get less significant and a new component appears at $\sim100$ TeV. The spatial distribution of the GCR intensity with an excess (7.2$\sigma$ pre-trial, 5.2$\sigma$ post-trial) and a deficit ($-5.8\sigma$ pre-trial) are observed in the 300 TeV anisotropy map, in a good agreement with IceCube's results at 400 TeV. Combining the Tibet results in the northern sky with IceCube's results in the southern sky, we establish a full-sky picture of the anisotropy in hundreds of TeV band. We further find that the amplitude of the first order anisotropy increases sharply above $\sim100$ TeV, indicating a new component of the anisotropy. All these results may shed new light on understanding the origin and propagation of GCRs.