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

Sgr A* was more active in the past
the CR spectrum at the source (Sgr A*) is relatively hard
the diffusion coefficient for the Galactic disk is small
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)

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