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Title: Sagittarius A* as an origin of the Galactic PeV cosmic rays?

Abstract

Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ('Pevatron'). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 10{sup 7} yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. Itmore » is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.« less

Authors:
 [1]; ;  [2]
  1. Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)
  2. Center for Particle and Gravitational Astrophysics, Department of Physics, Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
Publication Date:
OSTI Identifier:
22679905
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 04; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; ANISOTROPY; BUBBLES; COMPARATIVE EVALUATIONS; COSMIC RADIATION; DIFFUSION; DIFFUSION EQUATIONS; EMISSION; GALAXY NUCLEI; GAMMA RADIATION; LUMINOSITY; MILKY WAY; PEV RANGE; SPECTRA; SUPERNOVA REMNANTS

Citation Formats

Fujita, Yutaka, Murase, Kohta, and Kimura, Shigeo S., E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: murase@psu.edu, E-mail: szk323@psu.edu. Sagittarius A* as an origin of the Galactic PeV cosmic rays?. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/04/037.
Fujita, Yutaka, Murase, Kohta, & Kimura, Shigeo S., E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: murase@psu.edu, E-mail: szk323@psu.edu. Sagittarius A* as an origin of the Galactic PeV cosmic rays?. United States. doi:10.1088/1475-7516/2017/04/037.
Fujita, Yutaka, Murase, Kohta, and Kimura, Shigeo S., E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: murase@psu.edu, E-mail: szk323@psu.edu. Sat . "Sagittarius A* as an origin of the Galactic PeV cosmic rays?". United States. doi:10.1088/1475-7516/2017/04/037.
@article{osti_22679905,
title = {Sagittarius A* as an origin of the Galactic PeV cosmic rays?},
author = {Fujita, Yutaka and Murase, Kohta and Kimura, Shigeo S., E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: murase@psu.edu, E-mail: szk323@psu.edu},
abstractNote = {Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ('Pevatron'). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 10{sup 7} yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.},
doi = {10.1088/1475-7516/2017/04/037},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 04,
volume = 2017,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}