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Article: The Fermi Bubble as a source of cosmic rays in the energy range >10¹⁵ eV
Title | The Fermi Bubble as a source of cosmic rays in the energy range >10¹⁵ eV | ||||||||||
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Authors | |||||||||||
Keywords | Acceleration of particles Galaxies: jets Galaxy: halo Shock waves | ||||||||||
Issue Date | 2012 | ||||||||||
Publisher | Institute of Physics Publishing, Inc. The Journal's web site is located at http://iopscience.iop.org/0004-637X/ | ||||||||||
Citation | The Astrophysical Journal, 2012, v. 746 n. 2, article no. 116 How to Cite? | ||||||||||
Abstract | The Fermi Large Area Telescope has recently discovered two giant gamma-ray bubbles that extend north and south of the Galactic center with diameters and heights of the order of H 10kpc. We suggest that the periodic star capture processes by the Galactic supermassive black hole Sgr A*, with a capture rate of τ -1 cap 3 × 10 -5yr -1 and an energy release of W 3 × 10 52erg per capture, can result in hot plasma injecting into the Galactic halo at a wind velocity of u 10 8cms -1. The periodic injection of hot plasma can produce a series of shocks. Energetic protons in the bubble are re-accelerated when they interact with these shocks. We show that for energy larger than E > 10 15eV, the acceleration process can be better described by the stochastic second-order Fermi acceleration. We propose that hadronic cosmic rays (CRs) within the 'knee' of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Re-acceleration of these particles in the Fermi Bubble produces CRs beyond the knee. With a mean CR diffusion coefficient in this energy range in the bubble D B 3 × 10 30cm 2s -1, we can reproduce the spectral index of the spectrum beyond the knee and within it. The conversion efficiency from shock energy of the bubble into CR energy is about 10%. This model provides a natural explanation of the observed CR flux, spectral indices, and matching of spectra at the knee. © 2012. The American Astronomical Society. All rights reserved. | ||||||||||
Persistent Identifier | http://hdl.handle.net/10722/146408 | ||||||||||
ISSN | 2023 Impact Factor: 4.8 2023 SCImago Journal Rankings: 1.905 | ||||||||||
ISI Accession Number ID |
Funding Information: We are very grateful to A. M. Bykov, R. M. Crocker, A. D. Erlykin, Y. Uchiyama, and V. N. Zirakashvili for useful discussions, and to K. F. Sinkov who performed graphic and numerical illustrations of the Kompaneets solution presented in Section 3. D.O.C. and V. A. D. are partly supported by the NSC-RFBR Joint Research Project RP09N04 and 09-02-92000-HHC-a. K. S. C. is supported by the GRF Grants of the Government of the Hong Kong SAR under HKU 7011/10P. C. M. K. is supported by the Taiwan National Science Council Grants NSC 98-2923-M-008-01-MY3 and NSC 99-2112-M-008-015-MY3. W. H. I. is supported by the Taiwan National Science Council Grant NSC 97-2112-M-008-011-MY3 and Taiwan Ministry of Education under the Aim for Top University Program National Central University. |
DC Field | Value | Language |
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dc.contributor.author | Cheng, KS | en_US |
dc.contributor.author | Chernyshov, DO | en_US |
dc.contributor.author | Dogel, VA | en_US |
dc.contributor.author | Ko, CM | en_US |
dc.contributor.author | Ip, WH | en_US |
dc.contributor.author | Wang, Y | en_US |
dc.date.accessioned | 2012-04-24T07:52:12Z | - |
dc.date.available | 2012-04-24T07:52:12Z | - |
dc.date.issued | 2012 | en_US |
dc.identifier.citation | The Astrophysical Journal, 2012, v. 746 n. 2, article no. 116 | en_US |
dc.identifier.issn | 0004-637X | en_US |
dc.identifier.uri | http://hdl.handle.net/10722/146408 | - |
dc.description.abstract | The Fermi Large Area Telescope has recently discovered two giant gamma-ray bubbles that extend north and south of the Galactic center with diameters and heights of the order of H 10kpc. We suggest that the periodic star capture processes by the Galactic supermassive black hole Sgr A*, with a capture rate of τ -1 cap 3 × 10 -5yr -1 and an energy release of W 3 × 10 52erg per capture, can result in hot plasma injecting into the Galactic halo at a wind velocity of u 10 8cms -1. The periodic injection of hot plasma can produce a series of shocks. Energetic protons in the bubble are re-accelerated when they interact with these shocks. We show that for energy larger than E > 10 15eV, the acceleration process can be better described by the stochastic second-order Fermi acceleration. We propose that hadronic cosmic rays (CRs) within the 'knee' of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Re-acceleration of these particles in the Fermi Bubble produces CRs beyond the knee. With a mean CR diffusion coefficient in this energy range in the bubble D B 3 × 10 30cm 2s -1, we can reproduce the spectral index of the spectrum beyond the knee and within it. The conversion efficiency from shock energy of the bubble into CR energy is about 10%. This model provides a natural explanation of the observed CR flux, spectral indices, and matching of spectra at the knee. © 2012. The American Astronomical Society. All rights reserved. | - |
dc.language | eng | en_US |
dc.publisher | Institute of Physics Publishing, Inc. The Journal's web site is located at http://iopscience.iop.org/0004-637X/ | en_US |
dc.relation.ispartof | The Astrophysical Journal | en_US |
dc.rights | The Astrophysical Journal. Copyright © Institute of Physics Publishing, Inc. | en_US |
dc.subject | Acceleration of particles | - |
dc.subject | Galaxies: jets | - |
dc.subject | Galaxy: halo | - |
dc.subject | Shock waves | - |
dc.title | The Fermi Bubble as a source of cosmic rays in the energy range >10¹⁵ eV | en_US |
dc.type | Article | en_US |
dc.identifier.email | Cheng, KS: hrspksc@hkucc.hku.hk | en_US |
dc.identifier.email | Chernyshov, DO: chdmit@hku.hk | en_US |
dc.identifier.email | Dogel, VA: dogiel@bohr.physics.hku.hk | en_US |
dc.identifier.email | Ko, CM: cmko@hku.hk; cmko@astro.ncu.edu.tw | en_US |
dc.identifier.email | Wang, Y: yuwang20@hku.hk | en_US |
dc.identifier.authority | Cheng, KS=rp00675 | en_US |
dc.description.nature | published_or_final_version | - |
dc.identifier.doi | 10.1088/0004-637X/746/2/116 | - |
dc.identifier.scopus | eid_2-s2.0-84863176934 | - |
dc.identifier.hkuros | 199346 | en_US |
dc.identifier.volume | 746 | en_US |
dc.identifier.issue | 2, article no. 116 | en_US |
dc.identifier.eissn | 1538-4357 | - |
dc.identifier.isi | WOS:000300406300002 | - |
dc.publisher.place | United States | en_US |
dc.identifier.issnl | 0004-637X | - |