Beitrag in einer Fachzeitschrift

Details zur Publikation

Autor(en): Chakrabarty D, Tomsick JA, Grefenstette BW, Psaltis D, Bachetti M, Barret D, Boggs SE, Christensen FE, Craig WW, Fuerst F, Hailey CJ, Harrison FA, Kaspi VM, Miller JM, Nowak MA, Rana V, Stern D, Wik DR, Wilms J, Zhang WW
Zeitschrift: Astrophysical Journal
Jahr der Veröffentlichung: 2014
Band: 797
Heftnummer: 2
ISSN: 0004-637X


The 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 x 10(33) D-kpc(2) erg s(-1), with similar or equal to 60% 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 kT(e) = 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.

FAU-Autoren / FAU-Herausgeber

Wilms, Jörn Prof. Dr.
Professur für Astronomie und Astrophysik

Autor(en) der externen Einrichtung(en)
California Institute of Technology (Caltech)
Columbia University
Massachusetts Institute of Technology (MIT)
McGill University
National Aeronautics and Space Administration (NASA)
Technical University of Denmark / Danmarks Tekniske Universitet (DTU)
Université Toulouse III - Paul Sabatier
University of Arizona
University of California, Berkeley
University of Michigan


Chakrabarty, D., Tomsick, J.A., Grefenstette, B.W., Psaltis, D., Bachetti, M., Barret, D.,... Zhang, W.W. (2014). A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4. Astrophysical Journal, 797(2). https://dx.doi.org/10.1088/0004-637X/797/2/92

Chakrabarty, Deepto, et al. "A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4." Astrophysical Journal 797.2 (2014).


Zuletzt aktualisiert 2019-19-04 um 09:08