A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4
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 o...
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| Format: | Article |
| Language: | en_US |
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Institute of Physics/American Astronomical Society
2015
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| Online Access: | http://hdl.handle.net/1721.1/95685 https://orcid.org/0000-0001-8804-8946 |
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| author | Chakrabarty, Deepto Tomsick, John A. Grefenstette, Brian W. Psaltis, Dimitrios Bachetti, Matteo Barret, Didier Boggs, Steven E. Christensen, Finn E. Craig, William W. Furst, Felix Hailey, Charles J. Harrison, Fiona A. Kaspi, Victoria Miller, Jon M. Nowak, Michael A. Rana, Vikram Stern, Daniel Wik, Daniel R. Wilms, Jörn Zhang, William W. |
| author2 | MIT Kavli Institute for Astrophysics and Space Research |
| author_facet | MIT Kavli Institute for Astrophysics and Space Research Chakrabarty, Deepto Tomsick, John A. Grefenstette, Brian W. Psaltis, Dimitrios Bachetti, Matteo Barret, Didier Boggs, Steven E. Christensen, Finn E. Craig, William W. Furst, Felix Hailey, Charles J. Harrison, Fiona A. Kaspi, Victoria Miller, Jon M. Nowak, Michael A. Rana, Vikram Stern, Daniel Wik, Daniel R. Wilms, Jörn Zhang, William W. |
| author_sort | Chakrabarty, Deepto |
| collection | MIT |
| description | 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 {superscript 33] D[2 over kpc] erg s[superscript –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 kT[subscript 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. |
| first_indexed | 2024-09-23T15:20:33Z |
| format | Article |
| id | mit-1721.1/95685 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T15:20:33Z |
| publishDate | 2015 |
| publisher | Institute of Physics/American Astronomical Society |
| record_format | dspace |
| spelling | mit-1721.1/956852022-09-29T14:18:43Z A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4 Chakrabarty, Deepto Tomsick, John A. Grefenstette, Brian W. Psaltis, Dimitrios Bachetti, Matteo Barret, Didier Boggs, Steven E. Christensen, Finn E. Craig, William W. Furst, Felix Hailey, Charles J. Harrison, Fiona A. Kaspi, Victoria Miller, Jon M. Nowak, Michael A. Rana, Vikram Stern, Daniel Wik, Daniel R. Wilms, Jörn Zhang, William W. MIT Kavli Institute for Astrophysics and Space Research Chakrabarty, Deepto Nowak, Michael A 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 {superscript 33] D[2 over kpc] erg s[superscript –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 kT[subscript 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. United States. National Aeronautics and Space Administration (NASA contract NNG08FD60C) United States. National Aeronautics and Space Administration (XMM-Newton Guest Observer program, NASA grant NNX13AB47G)) 2015-02-26T20:12:16Z 2015-02-26T20:12:16Z 2014-12 2014-03 Article http://purl.org/eprint/type/JournalArticle 1538-4357 http://hdl.handle.net/1721.1/95685 Chakrabarty, Deepto, John A. Tomsick, Brian W. Grefenstette, Dimitrios Psaltis, Matteo Bachetti, Didier Barret, Steven E. Boggs, et al. “A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4.” The Astrophysical Journal 797, no. 2 (December 3, 2014): 92. © 2014 American Astronomical Society. https://orcid.org/0000-0001-8804-8946 en_US http://dx.doi.org/10.1088/0004-637X/797/2/92 Astrophysical Journal Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf Institute of Physics/American Astronomical Society American Astronomical Society |
| spellingShingle | Chakrabarty, Deepto Tomsick, John A. Grefenstette, Brian W. Psaltis, Dimitrios Bachetti, Matteo Barret, Didier Boggs, Steven E. Christensen, Finn E. Craig, William W. Furst, Felix Hailey, Charles J. Harrison, Fiona A. Kaspi, Victoria Miller, Jon M. Nowak, Michael A. Rana, Vikram Stern, Daniel Wik, Daniel R. Wilms, Jörn Zhang, William W. A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4 |
| title | A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4 |
| title_full | A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4 |
| title_fullStr | A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4 |
| title_full_unstemmed | A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4 |
| title_short | A HARD X-RAY POWER-LAW SPECTRAL CUTOFF IN CENTAURUS X-4 |
| title_sort | hard x ray power law spectral cutoff in centaurus x 4 |
| url | http://hdl.handle.net/1721.1/95685 https://orcid.org/0000-0001-8804-8946 |
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