Cosmic ray spectra and anisotropy under anisotropic propagation model with spiral galactic sources

TL;DR

This paper explores cosmic ray spectra and anisotropy using anisotropic propagation models with spiral galactic sources, incorporating local sources and magnetic fields to better match observations from GeV to PeV energies.

Contribution

It introduces a spiral distribution of galactic sources in anisotropic propagation models, accounting for local sources and magnetic fields, to improve the understanding of cosmic ray spectra and anisotropy.

Findings

Both spiral and axisymmetric source models reproduce observed spectra and anisotropy.

The spiral source model requires a larger diffusion coefficient and has harder spectral indices.

Inclusion of the Geminga source and magnetic field effects explains spectral hardening and anisotropy complexities.

Abstract

In our previous work, we have investigated Galactic cosmic ray (GCR) spectra and anisotropy from 100 GeV to PeV, under anisotropic propagation model with axisymmetric distributed galactic sources. Numerous observational evidence have indicated that the Milky Way is a typical spiral galaxy. In this work, we further utilize anisotropic propagation models with spiral galactic sources to investigate spectra and anisotropy of CRs. During the calculation process, we employ the spatially dependent diffusion (SDP) model with different diffusion coefficients for the inner and outer halo, while the background CR sources is spiral distribution. To better explain the anomalous observations of nuclear spectral hardening at $ {\cal R}\sim$ 200 GV and the complicated energy dependence of anisotropy from GeV to PeV, we introduce the contribution of the Geminga nearby source. Additionally, we incorporate the impact of the local regular magnetic field (LRMF) and the corresponding anisotropic diffusion on large-scale anisotropy within the SDP model. By comparing the spiral and axisymmetric distribution models of background sources, it is found that both of them can well reproduce the CR spectra and anisotropy from 100 GeV-PeV. However, their propagation parameters are different. The diffusion coefficient with spiral distribution of CR sources is larger than that with axisymmetric distribution, and its spectral indices are also harder. Future high-precision measurements of CR anisotropy, such as LHAASO experiment, will be crucial in evaluating the validity of our proposed model.