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Unconventional origin of supersoft X-ray emission from a white dwarf binary

Unconventional origin of supersoft X-ray emission from a white dwarf binary
Unconventional origin of supersoft X-ray emission from a white dwarf binary

Supersoft X-ray sources are stellar objects that emit X-rays with temperatures of about 1 million kelvin and luminosities well in excess of what can be produced by stellar coronae. It has generally been presumed that the objects in this class are binary star systems in which mass transfer leads to nuclear fusion on the surface of a white dwarf. Classical novae—the runaway fusion events on the surfaces of white dwarfs—generally have supersoft phases, and it is often stated that the bright steady supersoft X-ray sources seen from white dwarfs accreting mass at a high rate are undergoing steady nuclear fusion. Here, we report the discovery of a transient supersoft source in the Small Magellanic Cloud without any signature of nuclear fusion having taken place. This discovery indicates that the X-ray emission probably comes from a ‘spreading layer’  —a belt on the surface of the white dwarf near the inner edge of the accretion disk in which a large fraction of the total accretion energy is emitted—and (albeit more tentatively) that the accreting white dwarf is relatively massive. We thus establish that the presence of a supersoft source cannot always be used as a tracer of nuclear fusion, in contradiction with decades-old consensus about the nature of supersoft emission.

2397-3366
173-177
Maccarone, Thomas J.
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Nelson, Thomas J.
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Brown, Peter J.
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Mukai, Koji
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Charles, Philip A.
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Rajoelimanana, Andry
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Buckley, David A.H.
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Strader, Jay
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Chomiuk, Laura
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Britt, Christopher T.
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Jha, Saurabh W.
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Mróz, Przemek
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Udalski, Andrzej
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Szymański, Michal K.
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Soszyński, Igor
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Poleski, Radosław
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Kozłowski, Szymon
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Pietrukowicz, Paweł
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Skowron, Jan
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Ulaczyk, Krzysztof
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Maccarone, Thomas J.
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Nelson, Thomas J.
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Brown, Peter J.
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Mukai, Koji
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Charles, Philip A.
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Rajoelimanana, Andry
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Buckley, David A.H.
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Strader, Jay
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Chomiuk, Laura
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Britt, Christopher T.
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Jha, Saurabh W.
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Mróz, Przemek
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Udalski, Andrzej
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Szymański, Michal K.
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Soszyński, Igor
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Poleski, Radosław
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Kozłowski, Szymon
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Pietrukowicz, Paweł
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Skowron, Jan
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Ulaczyk, Krzysztof
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Maccarone, Thomas J., Nelson, Thomas J., Brown, Peter J., Mukai, Koji, Charles, Philip A., Rajoelimanana, Andry, Buckley, David A.H., Strader, Jay, Chomiuk, Laura, Britt, Christopher T., Jha, Saurabh W., Mróz, Przemek, Udalski, Andrzej, Szymański, Michal K., Soszyński, Igor, Poleski, Radosław, Kozłowski, Szymon, Pietrukowicz, Paweł, Skowron, Jan and Ulaczyk, Krzysztof (2019) Unconventional origin of supersoft X-ray emission from a white dwarf binary. Nature Astronomy, 3 (2), 173-177. (doi:10.1038/s41550-018-0639-1).

Record type: Letter

Abstract

Supersoft X-ray sources are stellar objects that emit X-rays with temperatures of about 1 million kelvin and luminosities well in excess of what can be produced by stellar coronae. It has generally been presumed that the objects in this class are binary star systems in which mass transfer leads to nuclear fusion on the surface of a white dwarf. Classical novae—the runaway fusion events on the surfaces of white dwarfs—generally have supersoft phases, and it is often stated that the bright steady supersoft X-ray sources seen from white dwarfs accreting mass at a high rate are undergoing steady nuclear fusion. Here, we report the discovery of a transient supersoft source in the Small Magellanic Cloud without any signature of nuclear fusion having taken place. This discovery indicates that the X-ray emission probably comes from a ‘spreading layer’  —a belt on the surface of the white dwarf near the inner edge of the accretion disk in which a large fraction of the total accretion energy is emitted—and (albeit more tentatively) that the accreting white dwarf is relatively massive. We thus establish that the presence of a supersoft source cannot always be used as a tracer of nuclear fusion, in contradiction with decades-old consensus about the nature of supersoft emission.

Full text not available from this repository.

More information

Accepted/In Press date: 12 October 2018
e-pub ahead of print date: 3 December 2018
Published date: 1 February 2019

Identifiers

Local EPrints ID: 428321
URI: http://eprints.soton.ac.uk/id/eprint/428321
ISSN: 2397-3366
PURE UUID: 04194903-92e2-45c0-b0c1-baa08cdc71f6

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Date deposited: 21 Feb 2019 17:30
Last modified: 07 Oct 2020 00:44

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Contributors

Author: Thomas J. Maccarone
Author: Thomas J. Nelson
Author: Peter J. Brown
Author: Koji Mukai
Author: Andry Rajoelimanana
Author: David A.H. Buckley
Author: Jay Strader
Author: Laura Chomiuk
Author: Christopher T. Britt
Author: Saurabh W. Jha
Author: Przemek Mróz
Author: Andrzej Udalski
Author: Michal K. Szymański
Author: Igor Soszyński
Author: Radosław Poleski
Author: Szymon Kozłowski
Author: Paweł Pietrukowicz
Author: Jan Skowron
Author: Krzysztof Ulaczyk

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