A three-component model for cosmic ray spectrum and dipole anisotropy

Abstract

ABSTRACT Using a three-component, multiscale diffusion model, we show that the cosmic ray (CR) proton and helium spectra and the dipole anisotropy can be explained with reasonable parameters. The model includes a nearby source associated with the supernova remnant (SNR) that gave rise to the Geminga pulsar, a source at the Galactic Centre, and a component associated with the Galactic disc. The CR flux below TeV is dominated by the disc component. The centre source with a continuous injection of CRs starting about 18 Myr ago is needed to explain the anisotropy above 100 TeV. With the assumption of universal CR spectra injected by all SNRs, the nearby source can produce a TeV spectral bump observed at Earth via slow diffusion across the interstellar magnetic field, which needs to have an angle θ ≈ 5° between the field line and the line of sight towards the source, and have weak magnetic turbulence with the Alfvén Mach number MA ≈ 0.1. Considering the modulation of the Galactic-scale anisotropy by this magnetic field, in a quasi-local approach the field may be directed at a right ascension about −90° and a declination about −7.4° in the equatorial coordinate system.