A Three-component Model for Cosmic-ray Spectrum and Dipole Anisotropy

Abstract

Using a three-component, multi-scale 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 center, and a component associated with the Galactic disk. The CR flux below TeV is dominated by the disk component. The center 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 $\theta \approx 5^{\circ }$ between the field line and the line of sight toward the source, and have weak magnetic turbulence with the Alfvén Mach number $M_{\text{A}}\approx 0.1$. 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 $-90^{\circ }$ and a declination about $-7.4^{\circ }$ in the equatorial coordinate system.

arXiv commentSubmitted to MNRAS

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• Direct measurements of cosmic rays and their possible interpretations
• Quantitative study of the hardening in the Alpha Magnetic Spectrometer nuclei spectra at a few hundred GV
• Influence of interstellar environment near the solar system on cosmic-ray spectra and dipole anisotropy