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Conference Paper: On the origin of annihilation emission from the Galactic Center

TitleOn the origin of annihilation emission from the Galactic Center
Authors
KeywordsBlack Hole
Comic Rays : General
Galaxies : Gamma-Rays
Galaxy : Center
Radiation Mechanisms : Nonthermal
Issue Date2006
Citation
European Space Agency, (Special Publication) Esa Sp, 2006 n. 622 SP, p. 41-48 How to Cite?
AbstractBoth diffuse high energy gamma-rays and an extended electron-positron annihilation line emission have been observed in the Galactic Center (GC) region. Although X-ray observations indicate that the galactic black hole Sgr A* is inactive now, we suggest that Sgr A* can become active when a captured star is tidally disrupted and matter is accreted into the black hole. As a consequence the galactic black hole could be a powerful source of relativistic protons. We are able to explain the current observed diffuse gamma-rays and the very detailed 511 keV annihilation line of secondary positrons by p - p collisions of such protons, with appropriate injection times and energy. Relativistic protons could have been injected into the ambient material if the black hole captured a 50M ⊙star at several tens million years ago. An alternative possibility is that the black hole continues to capture stars with ∼1M ⊙ every hundred thousand years. Secondary positrons produced by p -p collisions at energies ≥ 30 MeV are cooled down to thermal energies by Coulomb collisions, and annihilate in the warm neutral and ionized phases of the interstellar medium with temperatures about several eV, because the annihilation cross-section reaches its maximum at these temperatures. It takes about ten million years for the positrons to cool down to thermal temperatures so they can diffuse into a very large extended region around the Galactic center. A much more recent star capture may be also able to account for recent TeV observations within 10 pc of the galactic center as well as for the unidentified GeV gamma-ray sources found by EGRET at GC. The spectral difference between the GeV flux and the TeV flux could be explained naturally in this model as well.
Persistent Identifierhttp://hdl.handle.net/10722/176190
ISSN
References

 

DC FieldValueLanguage
dc.contributor.authorCheng, KSen_US
dc.contributor.authorChernyshov, DOen_US
dc.contributor.authorDogiel, VAen_US
dc.date.accessioned2012-11-26T09:06:42Z-
dc.date.available2012-11-26T09:06:42Z-
dc.date.issued2006en_US
dc.identifier.citationEuropean Space Agency, (Special Publication) Esa Sp, 2006 n. 622 SP, p. 41-48en_US
dc.identifier.issn0379-6566en_US
dc.identifier.urihttp://hdl.handle.net/10722/176190-
dc.description.abstractBoth diffuse high energy gamma-rays and an extended electron-positron annihilation line emission have been observed in the Galactic Center (GC) region. Although X-ray observations indicate that the galactic black hole Sgr A* is inactive now, we suggest that Sgr A* can become active when a captured star is tidally disrupted and matter is accreted into the black hole. As a consequence the galactic black hole could be a powerful source of relativistic protons. We are able to explain the current observed diffuse gamma-rays and the very detailed 511 keV annihilation line of secondary positrons by p - p collisions of such protons, with appropriate injection times and energy. Relativistic protons could have been injected into the ambient material if the black hole captured a 50M ⊙star at several tens million years ago. An alternative possibility is that the black hole continues to capture stars with ∼1M ⊙ every hundred thousand years. Secondary positrons produced by p -p collisions at energies ≥ 30 MeV are cooled down to thermal energies by Coulomb collisions, and annihilate in the warm neutral and ionized phases of the interstellar medium with temperatures about several eV, because the annihilation cross-section reaches its maximum at these temperatures. It takes about ten million years for the positrons to cool down to thermal temperatures so they can diffuse into a very large extended region around the Galactic center. A much more recent star capture may be also able to account for recent TeV observations within 10 pc of the galactic center as well as for the unidentified GeV gamma-ray sources found by EGRET at GC. The spectral difference between the GeV flux and the TeV flux could be explained naturally in this model as well.en_US
dc.languageengen_US
dc.relation.ispartofEuropean Space Agency, (Special Publication) ESA SPen_US
dc.subjectBlack Holeen_US
dc.subjectComic Rays : Generalen_US
dc.subjectGalaxies : Gamma-Raysen_US
dc.subjectGalaxy : Centeren_US
dc.subjectRadiation Mechanisms : Nonthermalen_US
dc.titleOn the origin of annihilation emission from the Galactic Centeren_US
dc.typeConference_Paperen_US
dc.identifier.emailCheng, KS: hrspksc@hkucc.hku.hken_US
dc.identifier.authorityCheng, KS=rp00675en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.scopuseid_2-s2.0-45749149660en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-45749149660&selection=ref&src=s&origin=recordpageen_US
dc.identifier.issue622 SPen_US
dc.identifier.spage41en_US
dc.identifier.epage48en_US
dc.identifier.scopusauthoridCheng, KS=9745798500en_US
dc.identifier.scopusauthoridChernyshov, DO=14059433800en_US
dc.identifier.scopusauthoridDogiel, VA=6603566238en_US

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