. (2009) Swift x-ray and ultraviolet monitoring of the classical Nova V458 Vul (Nova Vul 2007). The Astrophysical Journal, Vol.137 (No.5). pp. 4160-4168. ISSN 0004-637X

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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 x 10(34) erg s(-1) during days 71-140. The X-ray spectrum at this time requires a low Fe abundance (0.2(-0.1)(+ 0.3) 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(-5)(+9) 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.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Stars, New, Cataclysmic variable stars
Journal or Publication Title:	The Astrophysical Journal
Publisher:	Institute of Physics Publishing, Inc.
ISSN:	0004-637X
Date:	May 2009
Volume:	Vol.137
Number:	No.5
Number of Pages:	9
Page Range:	pp. 4160-4168
Identification Number:	10.1088/0004-6256/137/5/4160
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	United States. National Aeronautics and Space Administration (NASA), National Science Foundation (U.S.) (NSF), Science and Technology Facilities Council (Great Britain) (STFC)
Grant number:	PF5-60039 (NASA), PF6-70044 (NASA), NAS8-03060 (NASA), NAS8-39073 (NASA)
URI:	http://wrap.warwick.ac.uk/id/eprint/28178

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