Sagittarius A* as an Origin of the Galactic TeV-PeV Cosmic Rays?

Fujita et al. (2016) explore the possibility that Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, significantly contributes to the observed TeV-PeV cosmic rays (CRs) as a Galactic PeV particle accelerator ("Pevatron").


They show that a large number of TeV-PeV CRs may have been injected from Sgr A*, and that those CRs may have filled in the Galactic halo and some of them may have entered the Galactic disk.

Based on a diffusion-halo model, they solve diffusion equations for the CRs and compare the results with the CR spectrum and the anisotropy observed on the Earth as well as the diffuse gamma-ray emission from the Central Molecular Zone (CMZ) surrounding Sgr A*.

Image: This Chandra image shows the region around Sgr A* in low, medium, and high-energy X-rays that have been colored red, green, and blue respectively. Sgr A* is located within the white area in the center of the image. The blue and orange plumes around that area may be the remains of outbursts from Sgr A* that occurred millions of years ago. Credit: NASA/CXC/Univ. of Wisconsin/Y.Bai. et al.

They find that the CR spectrum, the anisotropy and the recent gamma-ray observations with the High Energy Stereoscopic System (HESS) can be explained simultaneously if

1. Sgr A* was more active in the past
2. the CR spectrum at the source (Sgr A*) is relatively hard
3. the diffusion coefficient for the Galactic disk is small
4. the energy dependence of the diffusion coefficient is different between the CMZ and the halo.

• Fujita et al 2016 (preprint) - Sagittarius A* as an Origin of the Galactic TeV-PeV Cosmic Rays? (arXiv)