A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR
We report on NuSTAR and Swift observations of a soft state of the neutron star low-mass X-ray binary GS 1826-24, commonly known as the "clocked" burster. The transition to the soft state was recorded in 2014 June through an increase of the 2-20 keV source intensity measured by MAXI, simult...
| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Article |
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American Astronomical Society
2018
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| Online Access: | http://hdl.handle.net/1721.1/114396 https://orcid.org/0000-0001-8804-8946 |
| _version_ | 1826197137668440064 |
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| author | Chenevez, J. Galloway, D. K. in ’t Zand, J. J. M. Tomsick, J. A. Barret, D. Fürst, F. Boggs, S. E. Christensen, F. E. Craig, W. W. Hailey, C. J. Harrison, F. A. Romano, P. Stern, D. Zhang, W. W. Chakrabarty, Deepto |
| author2 | Massachusetts Institute of Technology. Department of Physics |
| author_facet | Massachusetts Institute of Technology. Department of Physics Chenevez, J. Galloway, D. K. in ’t Zand, J. J. M. Tomsick, J. A. Barret, D. Fürst, F. Boggs, S. E. Christensen, F. E. Craig, W. W. Hailey, C. J. Harrison, F. A. Romano, P. Stern, D. Zhang, W. W. Chakrabarty, Deepto |
| author_sort | Chenevez, J. |
| collection | MIT |
| description | We report on NuSTAR and Swift observations of a soft state of the neutron star low-mass X-ray binary GS 1826-24, commonly known as the "clocked" burster. The transition to the soft state was recorded in 2014 June through an increase of the 2-20 keV source intensity measured by MAXI, simultaneous with a decrease of the 15-50 keV intensity measured by Swift/BAT. The episode lasted approximately two months, after which the source returned to its usual hard state. We analyze the broadband spectrum measured by Swift/XRT and NuSTAR and estimate the accretion rate during the soft episode to be ≈13% [dot over m][subscript Edd], within the range of previous observations. However, the best-fit spectral model, adopting the double Comptonization used previously, exhibits significantly softer components. We detect seven type-I X-ray bursts, all significantly weaker (and with shorter rise and decay times) than observed pr eviously. The burst profiles and recurrence times vary significantly, ruling out the regular bursts that are typical for this source. One burst exhibited photospheric radius expansion and we estimate the source distance as (5.7 ± 0.2) ξ [superscript -1/2][subscript b] kpc, where ξ[subscript b] parameterizes the possible anisotropy of the burst emission. The observed soft state may most likely be interpreted as a change in accretion geometry at about similar bolometric luminosity as in the hard state. The different burst behavior can therefore be attributed to this change in accretion flow geometry, but the fundamental cause and process for this effect remain unclear. Key words: accretion, accretion disks – binaries: close – stars: neutron – X-rays: bursts – X-rays:
individual (GS 1826–24) |
| first_indexed | 2024-09-23T10:43:04Z |
| format | Article |
| id | mit-1721.1/114396 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T10:43:04Z |
| publishDate | 2018 |
| publisher | American Astronomical Society |
| record_format | dspace |
| spelling | mit-1721.1/1143962022-09-27T14:30:19Z A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR Chenevez, J. Galloway, D. K. in ’t Zand, J. J. M. Tomsick, J. A. Barret, D. Fürst, F. Boggs, S. E. Christensen, F. E. Craig, W. W. Hailey, C. J. Harrison, F. A. Romano, P. Stern, D. Zhang, W. W. Chakrabarty, Deepto Massachusetts Institute of Technology. Department of Physics MIT Kavli Institute for Astrophysics and Space Research Chakrabarty, Deepto We report on NuSTAR and Swift observations of a soft state of the neutron star low-mass X-ray binary GS 1826-24, commonly known as the "clocked" burster. The transition to the soft state was recorded in 2014 June through an increase of the 2-20 keV source intensity measured by MAXI, simultaneous with a decrease of the 15-50 keV intensity measured by Swift/BAT. The episode lasted approximately two months, after which the source returned to its usual hard state. We analyze the broadband spectrum measured by Swift/XRT and NuSTAR and estimate the accretion rate during the soft episode to be ≈13% [dot over m][subscript Edd], within the range of previous observations. However, the best-fit spectral model, adopting the double Comptonization used previously, exhibits significantly softer components. We detect seven type-I X-ray bursts, all significantly weaker (and with shorter rise and decay times) than observed pr eviously. The burst profiles and recurrence times vary significantly, ruling out the regular bursts that are typical for this source. One burst exhibited photospheric radius expansion and we estimate the source distance as (5.7 ± 0.2) ξ [superscript -1/2][subscript b] kpc, where ξ[subscript b] parameterizes the possible anisotropy of the burst emission. The observed soft state may most likely be interpreted as a change in accretion geometry at about similar bolometric luminosity as in the hard state. The different burst behavior can therefore be attributed to this change in accretion flow geometry, but the fundamental cause and process for this effect remain unclear. Key words: accretion, accretion disks – binaries: close – stars: neutron – X-rays: bursts – X-rays: individual (GS 1826–24) 2018-03-27T15:36:39Z 2018-03-27T15:36:39Z 2017-02 2015-09 2018-02-16T14:15:14Z Article http://purl.org/eprint/type/JournalArticle 1538-4357 0004-637X http://hdl.handle.net/1721.1/114396 Chenevez, J., et al. “A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR.” The Astrophysical Journal, vol. 818, no. 2, Feb. 2016, p. 135. © 2016 The American Astronomical Society https://orcid.org/0000-0001-8804-8946 http://dx.doi.org/10.3847/0004-637X/818/2/135 The 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 American Astronomical Society |
| spellingShingle | Chenevez, J. Galloway, D. K. in ’t Zand, J. J. M. Tomsick, J. A. Barret, D. Fürst, F. Boggs, S. E. Christensen, F. E. Craig, W. W. Hailey, C. J. Harrison, F. A. Romano, P. Stern, D. Zhang, W. W. Chakrabarty, Deepto A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR |
| title | A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR |
| title_full | A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR |
| title_fullStr | A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR |
| title_full_unstemmed | A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR |
| title_short | A SOFT X-RAY SPECTRAL EPISODE FOR THE CLOCKED BURSTER, GS 1826–24 AS MEASURED BY SWIFT AND NuSTAR |
| title_sort | soft x ray spectral episode for the clocked burster gs 1826 24 as measured by swift and nustar |
| url | http://hdl.handle.net/1721.1/114396 https://orcid.org/0000-0001-8804-8946 |
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