The origin of cosmic rays (CRs) has been discussed for a long time. We 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''). We have investigated Sgr A* as a Pevatron and studied neutrino and gamma-ray emissions from escaping CRs. Moreover, we 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, we 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*. We 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, and (4) the energy dependence of the diffusion coefficient is different betweenthe CMZ and the halo.
KMI Colloquium
"Sagittarius A* as an Origin of the Galactic Cosmic Rays?"
Yutaka Fujita
(Osaka University)
July 27, 2016 (Wed) 17:00-
KMI Science Symposia (ES635)
Abstract: