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Article: The origin of gamma rays from globular clusters

TitleThe origin of gamma rays from globular clusters
Authors
KeywordsGamma Rays: Stars
Globular Clusters: General
Globular Clusters: Individual (47 Tuc, Terzan 5)
Pulsars: General
Issue Date2010
PublisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205
Citation
Astrophysical Journal Letters, 2010, v. 723 n. 2, p. 1219-1230 How to Cite?
AbstractFermi has detected gamma-ray emission from eight globular clusters (GCs). It is commonly believed that the energy sources of these gamma rays are millisecond pulsars (MSPs) inside GCs. Also it has been standard to explain the spectra of most Fe r m i Large Area Telescope pulsars including MSPs resulting from the curvature radiation (CR) of relativistic electrons/positrons inside the pulsar magnetosphere. Therefore, gamma rays from GCs are expected to be the collection of CR from all MSPs inside the clusters. However, the angular resolution is not high enough to pinpoint the nature of the emission. In this paper, we calculate the gamma rays produced by the inverse Compton (IC) scattering between relativistic electrons/positrons in the pulsar wind of MSPs in the GCs and background soft photons including cosmic microwave/relic photons, background star lights in the clusters, the galactic infrared photons, and the galactic star lights. We show that the gamma-ray spectrum from 47 Tucanae can be explained equally well by upward scattering of either the relic photons, the galactic infrared photons, or the galactic star lights, whereas the gamma-ray spectra from the other seven GCs are best fitted by the upward scattering of either the galactic infrared photons or the galactic star lights. We also find that the observed gamma-ray luminosity is correlated better with the combined factor of the encounter rate and the background soft photon energy density. Therefore, the IC scattering may also contribute to the observed gamma-ray emission from GCs detected by Fe r m i in addition to the standard CR process. Furthermore, we find that the emission region of high-energy photons from GCs produced by the IC scattering is substantially larger than the cores of GCs with a radius >10 pc. The diffuse radio and X-rays emitted from GCs can also be produced by the synchrotron radiation and IC scattering, respectively. We suggest that future observations including radio, X-rays, and gamma rays with energy higher than 10 GeV and better angular resolution can provide better constraints for the models. © 2010. The American Astronomical Society.
Persistent Identifierhttp://hdl.handle.net/10722/175182
ISSN
2015 Impact Factor: 5.487
2015 SCImago Journal Rankings: 3.369
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorCheng, KSen_US
dc.contributor.authorChernyshov, DOen_US
dc.contributor.authorDogiel, VAen_US
dc.contributor.authorHui, CYen_US
dc.contributor.authorKong, AKHen_US
dc.date.accessioned2012-11-26T08:49:41Z-
dc.date.available2012-11-26T08:49:41Z-
dc.date.issued2010en_US
dc.identifier.citationAstrophysical Journal Letters, 2010, v. 723 n. 2, p. 1219-1230en_US
dc.identifier.issn2041-8205en_US
dc.identifier.urihttp://hdl.handle.net/10722/175182-
dc.description.abstractFermi has detected gamma-ray emission from eight globular clusters (GCs). It is commonly believed that the energy sources of these gamma rays are millisecond pulsars (MSPs) inside GCs. Also it has been standard to explain the spectra of most Fe r m i Large Area Telescope pulsars including MSPs resulting from the curvature radiation (CR) of relativistic electrons/positrons inside the pulsar magnetosphere. Therefore, gamma rays from GCs are expected to be the collection of CR from all MSPs inside the clusters. However, the angular resolution is not high enough to pinpoint the nature of the emission. In this paper, we calculate the gamma rays produced by the inverse Compton (IC) scattering between relativistic electrons/positrons in the pulsar wind of MSPs in the GCs and background soft photons including cosmic microwave/relic photons, background star lights in the clusters, the galactic infrared photons, and the galactic star lights. We show that the gamma-ray spectrum from 47 Tucanae can be explained equally well by upward scattering of either the relic photons, the galactic infrared photons, or the galactic star lights, whereas the gamma-ray spectra from the other seven GCs are best fitted by the upward scattering of either the galactic infrared photons or the galactic star lights. We also find that the observed gamma-ray luminosity is correlated better with the combined factor of the encounter rate and the background soft photon energy density. Therefore, the IC scattering may also contribute to the observed gamma-ray emission from GCs detected by Fe r m i in addition to the standard CR process. Furthermore, we find that the emission region of high-energy photons from GCs produced by the IC scattering is substantially larger than the cores of GCs with a radius >10 pc. The diffuse radio and X-rays emitted from GCs can also be produced by the synchrotron radiation and IC scattering, respectively. We suggest that future observations including radio, X-rays, and gamma rays with energy higher than 10 GeV and better angular resolution can provide better constraints for the models. © 2010. The American Astronomical Society.en_US
dc.languageengen_US
dc.publisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205en_US
dc.relation.ispartofAstrophysical Journal Lettersen_US
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subjectGamma Rays: Starsen_US
dc.subjectGlobular Clusters: Generalen_US
dc.subjectGlobular Clusters: Individual (47 Tuc, Terzan 5)en_US
dc.subjectPulsars: Generalen_US
dc.titleThe origin of gamma rays from globular clustersen_US
dc.typeArticleen_US
dc.identifier.emailCheng, KS: hrspksc@hkucc.hku.hken_US
dc.identifier.authorityCheng, KS=rp00675en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.1088/0004-637X/723/2/1219en_US
dc.identifier.scopuseid_2-s2.0-78650093878en_US
dc.identifier.hkuros184979-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-78650093878&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume723en_US
dc.identifier.issue2en_US
dc.identifier.spage1219en_US
dc.identifier.epage1230en_US
dc.identifier.eissn1538-4357-
dc.identifier.isiWOS:000284093700022-
dc.publisher.placeUnited Kingdomen_US
dc.identifier.scopusauthoridCheng, KS=9745798500en_US
dc.identifier.scopusauthoridChernyshov, DO=14059433800en_US
dc.identifier.scopusauthoridDogiel, VA=6603566238en_US
dc.identifier.scopusauthoridHui, CY=12781234500en_US
dc.identifier.scopusauthoridKong, AKH=35185316600en_US

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