Bibcode
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.
Referencia bibliográfica
The Astronomical Journal, Volume 137, Issue 5, pp. 4160-4168 (2009).
Fecha de publicación:
5
2009
Número de citas
32
Número de citas referidas
28
Descripción
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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