Please use this identifier to cite or link to this item: http://hdl.handle.net/2289/7365
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dc.contributor.authorChakrabarty, Deepto-
dc.contributor.authorTomsick, John A.-
dc.contributor.authorRana, V-
dc.contributor.author+17 Co-Authors-
dc.date.accessioned2019-11-27T06:46:30Z-
dc.date.available2019-11-27T06:46:30Z-
dc.date.issued2014-12-20-
dc.identifier.citationThe Astrophysical Journal, 2014, Vol.797, p15en_US
dc.identifier.issn0004-637X-
dc.identifier.issn1538-4357(Online)-
dc.identifier.urihttp://hdl.handle.net/2289/7365-
dc.descriptionOpen Access.en_US
dc.description.abstractThe low-mass X-ray binary (LMXB) Cen X-4 is the brightest and closest (<1.2 kpc) quiescent neutron star transient. Previous 0.5-10 keV X-ray observations of Cen X-4 in quiescence identified two spectral components: soft thermal emission from the neutron star atmosphere and a hard power-law tail of unknown origin. We report here on a simultaneous observation of Cen X-4 with NuSTAR (3-79 keV) and XMM-Newton (0.3-10 keV) in 2013 January, providing the first sensitive hard X-ray spectrum of a quiescent neutron star transient. The 0.3-79 keV luminosity was 1.1× 1033 D^2_kpc erg s-1, with sime60% in the thermal component. We clearly detect a cutoff of the hard spectral tail above 10 keV, the first time such a feature has been detected in this source class. We show that thermal Comptonization and synchrotron shock origins for the hard X-ray emission are ruled out on physical grounds. However, the hard X-ray spectrum is well fit by a thermal bremsstrahlung model with kTe = 18 keV, which can be understood as arising either in a hot layer above the neutron star atmosphere or in a radiatively inefficient accretion flow. The power-law cutoff energy may be set by the degree of Compton cooling of the bremsstrahlung electrons by thermal seed photons from the neutron star surface. Lower thermal luminosities should lead to higher (possibly undetectable) cutoff energies. We compare Cen X-4's behavior with PSR J1023+0038, IGR J18245-2452, and XSS J12270-4859, which have shown transitions between LMXB and radio pulsar modes at a similar X-ray luminosity.en_US
dc.language.isoenen_US
dc.publisherIOP Sciences for The American Astronomical Societyen_US
dc.relation.urihttps://ui.adsabs.harvard.edu/abs/2014ApJ...797...92C/abstracten_US
dc.relation.urihttps://arxiv.org/abs/1403.6751en_US
dc.relation.urihttp://dx.doi.org/10.1088/0004-637X/797/2/92en_US
dc.rights2014, The American Astronomical Societyen_US
dc.subjectaccretionen_US
dc.subjectaccretion disksen_US
dc.subjectbinaries: closeen_US
dc.subjectstars: individual: Cen X-4en_US
dc.subjectstars: neutronen_US
dc.subjectX-rays: binariesen_US
dc.titleA Hard X-Ray Power-Law Spectral Cutoff in Centaurus X-4en_US
dc.typeArticleen_US
Appears in Collections:Research Papers (A&A)

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