Fangheng Zhang

In our previous work, we investigated the spectra and anisotropy of galactic cosmic rays (GCRs) under the assumption of an axisymmetric distribution of galactic sources. Currently, much observational evidence indicates that the Milky Way is a typical spiral galaxy. In this work, we further utilize an anisotropic propagation model under the framework of spiral distribution sources to study spectra and anisotropy. During the calculation process, we adopt the spatial-dependent propagation (SDP) model, while incorporating the contribution from the nearby Geminga source and the anisotropic diffusion of cosmic rays (CRs) induced by the local regular magnetic field (LRMF). By comparing the results of background sources with spiral and axisymmetric distribution models, it is found that both of them can well reproduce the CR spectra and anisotropy. However, there exist differences in their propagation parameters. The diffusion coefficient with spiral distribution is larger than that with axisymmetric distribution, and its spectral indices are slightly harder. To investigate the effects of a nearby Geminga source and LRMF on anisotropy, two-dimensional (2D) anisotropy sky maps under various contributing factors are compared. Below 100 TeV, the anisotropy is predominantly influenced by both the nearby Geminga source and the LRMF, causing the phase to align with the direction of the LRMF. Above 100 TeV, the background sources become dominant, resulting in the phase pointing towards the Galactic Center (GC). Future high-precision measurements of CR anisotropy and spectra, such as the LHAASO experiment, will be crucial in evaluating the validity of our proposed model.

The latest experimental measurements of cosmic rays (CRs) have discovered a series of anomalies, including the hardening of the nuclear spectra at R ∼200 GV followed by softening at R ∼10 TV and complicated energy dependence of anisotropy from GeV to PeV. Recent works have demonstrated nearby sources are crucial for these anomalies of spectra and anisotropy. In this work, we analyze the contributions of five nearby sources within 1 kpc around solar system to the spectra and anisotropy, finally find out which source is the best candidate source. In the calculation process, we also introduce the anisotropic diffusion of CRs induced by the local interstellar magnetic field (LIMF) nearby the solar system based on spatial-dependent propagation (SDP) model. As a result, we find Geminga SNR source can simultaneously account for CR spectra and anisotropy, whereas the other sources can not . Measurements of CR anisotropy and spectra by experiments such as LHAASO and HAWC are expected to test this scenario in the near future.