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Article: Diffuse x-ray emission in globular cluster cores

TitleDiffuse x-ray emission in globular cluster cores
Authors
KeywordsGlobular clusters: general
Pulsars: general
Stars: neutron
X-rays: stars
Issue Date2009
PublisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205
Citation
Astrophysical Journal Letters, 2009, v. 700 n. 2, p. 1233-1241 How to Cite?
AbstractThe unresolved X-ray emission in the cores of 10 globular clusters hosting millisecond pulsars is investigated. Subtraction of the known resolved point sources leads to detectable levels of unresolved emission in the core region of M28, NGC 6440, M62, and NGC 6752. The X-ray luminosities in the 0.3-8 keV energy band of this emission component were found to lie in the range 1.5 × 1031erg s-1 (NGC 6752) to 2.2 × 1032 erg s-1 (M28). The lowest limiting luminosity for X-ray source detections amongst these four clusters was 1.1 × 1030 erg s-1 for NGC 6752. The spectrum of the unresolved emission can be fit equally well by a power law, a thermal bremsstrahlung model, a blackbody plus power law, or a thermal bremsstrahlung model plus blackbody component. The unresolved emission is considered to arise from the cumulative contribution of active binaries, cataclysmic variables, and faint millisecond pulsars with their associated pulsar wind nebulae. In examining the available X-ray data, no evidence for any pulsar wind nebular emission in globular clusters is found. It is shown that the X-ray luminosity contribution of a faint source population based on an extrapolation of the luminosity function of detected point sources is compatible with the unresolved X-ray emission in the cores of NGC 6440 and NGC 6752. Adopting the same slope for the luminosity function for M62 as for NGC 6440 and NGC 6752 leads to a similar result for M62. For M28, the contribution from faint sources in the core can attain a level comparable with the observed value if a steeper slope is adopted. The characteristics on the faint source population as constrained by the properties of the unresolved X-ray emission are briefly discussed. © 2009 The American Astronomical Society.
Persistent Identifierhttp://hdl.handle.net/10722/80818
ISSN
2015 Impact Factor: 5.487
2015 SCImago Journal Rankings: 3.369
ISI Accession Number ID
Funding AgencyGrant Number
Croucher Foundation Postdoctoral Fellowship
GRF grant of Hong Kong GovernmentHKU700908P
Theoretical Institute for Advanced Research in Astrophysics (TIARA)
Funding Information:

C. Y. H. and K. S. C. were supported by the Croucher Foundation Postdoctoral Fellowship and a GRF grant of Hong Kong Government under HKU700908P, respectively. R. E. T. was supported in part by the Theoretical Institute for Advanced Research in Astrophysics (TIARA) operated under the Academia Sinica Institute of Astronomy & Astrophysics in Taipei, Taiwan.

References

 

DC FieldValueLanguage
dc.contributor.authorHui, CYen_HK
dc.contributor.authorCheng, KSen_HK
dc.contributor.authorTaam, REen_HK
dc.date.accessioned2010-09-06T08:10:37Z-
dc.date.available2010-09-06T08:10:37Z-
dc.date.issued2009en_HK
dc.identifier.citationAstrophysical Journal Letters, 2009, v. 700 n. 2, p. 1233-1241en_HK
dc.identifier.issn2041-8205en_HK
dc.identifier.urihttp://hdl.handle.net/10722/80818-
dc.description.abstractThe unresolved X-ray emission in the cores of 10 globular clusters hosting millisecond pulsars is investigated. Subtraction of the known resolved point sources leads to detectable levels of unresolved emission in the core region of M28, NGC 6440, M62, and NGC 6752. The X-ray luminosities in the 0.3-8 keV energy band of this emission component were found to lie in the range 1.5 × 1031erg s-1 (NGC 6752) to 2.2 × 1032 erg s-1 (M28). The lowest limiting luminosity for X-ray source detections amongst these four clusters was 1.1 × 1030 erg s-1 for NGC 6752. The spectrum of the unresolved emission can be fit equally well by a power law, a thermal bremsstrahlung model, a blackbody plus power law, or a thermal bremsstrahlung model plus blackbody component. The unresolved emission is considered to arise from the cumulative contribution of active binaries, cataclysmic variables, and faint millisecond pulsars with their associated pulsar wind nebulae. In examining the available X-ray data, no evidence for any pulsar wind nebular emission in globular clusters is found. It is shown that the X-ray luminosity contribution of a faint source population based on an extrapolation of the luminosity function of detected point sources is compatible with the unresolved X-ray emission in the cores of NGC 6440 and NGC 6752. Adopting the same slope for the luminosity function for M62 as for NGC 6440 and NGC 6752 leads to a similar result for M62. For M28, the contribution from faint sources in the core can attain a level comparable with the observed value if a steeper slope is adopted. The characteristics on the faint source population as constrained by the properties of the unresolved X-ray emission are briefly discussed. © 2009 The American Astronomical Society.en_HK
dc.languageengen_HK
dc.publisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205en_HK
dc.relation.ispartofAstrophysical Journal Lettersen_HK
dc.rightsThe Astrophysical Journal. Copyright © Institute of Physics Publishing, Inc.en_HK
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subjectGlobular clusters: generalen_HK
dc.subjectPulsars: generalen_HK
dc.subjectStars: neutronen_HK
dc.subjectX-rays: starsen_HK
dc.titleDiffuse x-ray emission in globular cluster coresen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0004-637X&volume=700&issue=2&spage=1233&epage=1241&date=2009&atitle=Diffuse+x-ray+emission+in+globular+cluster+coresen_HK
dc.identifier.emailCheng, KS: hrspksc@hkucc.hku.hken_HK
dc.identifier.authorityCheng, KS=rp00675en_HK
dc.description.naturepostprint-
dc.identifier.doi10.1088/0004-637X/700/2/1233en_HK
dc.identifier.scopuseid_2-s2.0-70449738184en_HK
dc.identifier.hkuros166035en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-70449738184&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume700en_HK
dc.identifier.issue2en_HK
dc.identifier.spage1233en_HK
dc.identifier.epage1241en_HK
dc.identifier.isiWOS:000268098100032-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridHui, CY=12781234500en_HK
dc.identifier.scopusauthoridCheng, KS=9745798500en_HK
dc.identifier.scopusauthoridTaam, RE=7003756329en_HK

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