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)

Comments

BOUNCING BLACK HOLES

Image: Illustration of a dusty supermassive black hole. Credit: ESA/NASA, the AVO project and Paolo Padovani Black holes could be bouncing stars as a consequence of quantum gravity: when the density of matter becomes high enough, quantum gravity effects generate sufficient pressure to compensate the matter's weight, the collapse ends, and matter bounces out. In a black hole, matter's collapse could stop before the central singularity is formed.

QUASARS AND THE COSMIC REIONIZATION

Credit: NASA/ESA Recently it has been suggested that quasars can be primarily responsible for the reionization of the universe.

A DARK MATTER HALO AS SOURCE OF GAMMA-RAYS?

Image: Illustration of a dark matter halo around the Milky Way. Credit: ESO/L. Calçada. The gamma-ray source 3FGL J2212.5+0703 shows evidence of being spatially extended. In a recent paper (Bertoni et al. 2016) the authors use a large sample of active galactic nuclei and other known gamma-rays sources as a control group, confirming, as expected, that statistically significant extension is rare among such objects. They argue that the most likely (non-dark matter) explanation for this apparent extension is a pair of bright gamma-ray sources that serendipitously lie very close to each other, and estimate that there is a chance probability of ~2% that such a pair would exist somewhere on the sky. If a gamma-ray source without detectable emission at other wavelengths were unambiguously determined to be spatially extended, it could not be explained by known astrophysics, and would constitute a smoking gun for dark matter particles annihilating in a nearby subhalo. The authors...

SpaceTime

Search This Blog