Continuing X-ray Emission of Nova Vul 2007

ATel #1603; J. J. Drake (Smithsonian Astrophysical Observatory), K. Page, J. Osborne, A. Beardmore (Leicester), J.-U. Ness, S. Starrfield (Arizona State), G. Schwarz (West Chester), M. Tsujimoto (Penn State), M. Barlow, R. Wesson (University College London), M. Bode (Liverpool John Moores), R. Corradi, P. Rodriguez-Gil (Instituto de Astrofisica de Canarias), J. Drew (Hertfordshire), B. Gaensicke, Daniel Steeghs (Warwick), C. Knigge (Southampton), D. Takai (Rikkyo), A. Zijlstra (Manchester)
on 5 Jul 2008; 14:19 UT
Credential Certification: Jeremy J. Drake (jdrake@cfa.harvard.edu)

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We report a new observation of Nova Vul 2007 (S. Nakano, IAUC 8861 ) obtained by the Swift X-ray Telescope (XRT) on 2008 June 18. The nova was detected at count rate of 0.023 count/s, representing a decline by a factor of 3 compared with Swift XRT observations obtained during 2007 November-December, and by about 50% compared with the previous observation obtained on 2007 December 27. The XRT spectrum is significantly softer than during the earlier epoch, with a ratio of X-ray counts in the 1-10 keV band to those in the 0.3-1 keV band having declined from about 1.0 to 0.4. The spectrum is largely consistent with models comprising a thermal plasma with temperature kT=1.8 +4.0/-0.8 keV combined with either a second cooler thermal plasma (kT=0.020 +0.007/-0.003 keV) or a blackbody (kT=0.020 +0.020/-0.001), with absorption corresponding to a cosmic composition and neutral hydrogen column density NH=(3.5+/-1.3)x10^21 cm^-2. A conspicuous discrepancy between observed and model spectra near 0.83 keV remains. This is coincident with the strong Fe XVII 2p6 1S0.0 - 2p5.3d 1P1.0 15.01 AA resonance transition. While ameliorated by addition of an arbitrary narrow line at this energy, this solution should be viewed with caution since raising the Fe abundance in the model fails to provide an equally satisfactory match. The unabsorbed X-ray flux in the 0.3-10 keV band during the observation was (7.3+/-0.8)e-10 erg cm^-2 s^-1, and the Swift Ultraviolet and Optical Telescope (UVOT) UVW1 magnitude was approximately 15.5.