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Swift X-ray and ultraviolet monitoring of the classical nova V458 VUL (Nova Vul 2007)

Swift X-ray and ultraviolet monitoring of the classical nova V458 VUL (Nova Vul 2007)
Swift X-ray and ultraviolet monitoring of the classical nova V458 VUL (Nova Vul 2007)
We describe the highly variable X-ray and UV emission of V458 Vul (Nova Vul 2007), observed by Swift between 1 and 422 days after outburst. Initially bright only in the UV, V458 Vul became a variable hard X-ray source due to optically thin thermal emission at kT = 0.64 keV with an X-ray band unabsorbed luminosity of 2.3 × 1034 erg s–1 during days 71-140. The X-ray spectrum at this time requires a low Fe abundance (0.2+0.3 –0.1 solar), consistent with a Suzaku measurement around the same time. On day 315 we find a new X-ray spectral component which can be described by a blackbody with temperature of kT = 23+9 –5 eV, while the previous hard X-ray component has declined by a factor of 3.8. The spectrum of this soft X-ray component resembles those typically seen in the class of supersoft sources (SSS) which suggests that the nova ejecta were starting to clear and/or that the white dwarf photosphere is shrinking to the point at which its thermal emission reaches into the X-ray band. We find a high degree of variability in the soft component with a flare rising by an order of magnitude in count rate in 0.2 days. In the following observations on days 342.4-383.6, the soft component was not seen, only to emerge again on day 397. The hard component continued to evolve, and we found an anticorrelation between the hard X-ray emission and the UV emission, yielding a Spearman rank probability of 97%. After day 397, the hard component was still present, was variable, and continued to fade at an extremely slow rate but could not be analyzed owing to pile-up contamination from the bright SSS component.
novae, cataclysmic variables, stars: individual (V458 Vul, V458 Vul)
4160
Ness, J.-U.
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Drake, J.J.
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Beardmore, A.P.
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Boyd, D.
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Bode, M.F.
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Brady, S.
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Evans, P.A.
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Gaensicke, B.T.
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Kitamoto, S.
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Knigge, C.
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Miller, I.
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Osborne, J.P.
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Page, K.L.
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Rodriguez-Gil, P.
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Schwarz, G.
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Staels, B.
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Steeghs, D.
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Takei, D.
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Tsujimoto, M.
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Wesson, R.
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Zijlstra, A.
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Ness, J.-U.
b517bbef-563e-4fd4-9873-96c281556ef7
Drake, J.J.
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Beardmore, A.P.
d72591c2-c08f-42b6-9f46-645aacb4e3e0
Boyd, D.
a9a18d6b-8f33-4025-9ba0-9de91b4924bd
Bode, M.F.
11930084-8f69-4282-b542-6f819303147a
Brady, S.
b8395d3b-2137-4f6d-a126-86c95cd0833d
Evans, P.A.
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Gaensicke, B.T.
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Kitamoto, S.
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Knigge, C.
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Miller, I.
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Osborne, J.P.
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Page, K.L.
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Rodriguez-Gil, P.
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Schwarz, G.
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Staels, B.
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Steeghs, D.
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Takei, D.
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Tsujimoto, M.
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Wesson, R.
06813094-f19d-484e-b60f-78f38455ca8b
Zijlstra, A.
efe6450b-3fa8-4744-8136-75911b38481d

Ness, J.-U., Drake, J.J., Beardmore, A.P., Boyd, D., Bode, M.F., Brady, S., Evans, P.A., Gaensicke, B.T., Kitamoto, S., Knigge, C., Miller, I., Osborne, J.P., Page, K.L., Rodriguez-Gil, P., Schwarz, G., Staels, B., Steeghs, D., Takei, D., Tsujimoto, M., Wesson, R. and Zijlstra, A. (2009) Swift X-ray and ultraviolet monitoring of the classical nova V458 VUL (Nova Vul 2007). The Astronomical Journal, 137 (5), 4160. (doi:10.1088/0004-6256/137/5/4160).

Record type: Article

Abstract

We describe the highly variable X-ray and UV emission of V458 Vul (Nova Vul 2007), observed by Swift between 1 and 422 days after outburst. Initially bright only in the UV, V458 Vul became a variable hard X-ray source due to optically thin thermal emission at kT = 0.64 keV with an X-ray band unabsorbed luminosity of 2.3 × 1034 erg s–1 during days 71-140. The X-ray spectrum at this time requires a low Fe abundance (0.2+0.3 –0.1 solar), consistent with a Suzaku measurement around the same time. On day 315 we find a new X-ray spectral component which can be described by a blackbody with temperature of kT = 23+9 –5 eV, while the previous hard X-ray component has declined by a factor of 3.8. The spectrum of this soft X-ray component resembles those typically seen in the class of supersoft sources (SSS) which suggests that the nova ejecta were starting to clear and/or that the white dwarf photosphere is shrinking to the point at which its thermal emission reaches into the X-ray band. We find a high degree of variability in the soft component with a flare rising by an order of magnitude in count rate in 0.2 days. In the following observations on days 342.4-383.6, the soft component was not seen, only to emerge again on day 397. The hard component continued to evolve, and we found an anticorrelation between the hard X-ray emission and the UV emission, yielding a Spearman rank probability of 97%. After day 397, the hard component was still present, was variable, and continued to fade at an extremely slow rate but could not be analyzed owing to pile-up contamination from the bright SSS component.

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More information

Published date: May 2009
Keywords: novae, cataclysmic variables, stars: individual (V458 Vul, V458 Vul)

Identifiers

Local EPrints ID: 144175
URI: http://eprints.soton.ac.uk/id/eprint/144175
PURE UUID: 2f53458b-c657-4677-a305-298f8c5eb58a

Catalogue record

Date deposited: 19 Apr 2010 10:19
Last modified: 08 Nov 2021 18:10

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Contributors

Author: J.-U. Ness
Author: J.J. Drake
Author: A.P. Beardmore
Author: D. Boyd
Author: M.F. Bode
Author: S. Brady
Author: P.A. Evans
Author: B.T. Gaensicke
Author: S. Kitamoto
Author: C. Knigge
Author: I. Miller
Author: J.P. Osborne
Author: K.L. Page
Author: P. Rodriguez-Gil
Author: G. Schwarz
Author: B. Staels
Author: D. Steeghs
Author: D. Takei
Author: M. Tsujimoto
Author: R. Wesson
Author: A. Zijlstra

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