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Authors: 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.
Zijlstra, A.
First Published: 30-Mar-2009
Publisher: American Astronomical Society (IOP Publishing)
Citation: Astronomical Journal, 2009, 137 (5), pp. 4160-4168
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 × 10[superscript: 34] erg s[superscript: –1] during days 71-140. The X-ray spectrum at this time requires a low Fe abundance (0.2[superscript: +0.3] [subscript: –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[superscript: +9] [subscript: –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.
DOI Link: 10.1088/0004-6256/137/5/4160
ISSN: 0004-6256
eISSN: 1538-3881
Version: Publisher Version
Type: Journal Article
Rights: Copyright © 2009, The American Astronomical Society. All rights reserved.. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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