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ATEL # 1184; G. Sala (MPE), M. Hernanz (IEEC-CSIC), C. Ferri (IEEC-CSIC)
on 17 Aug 2007; 15:21 UT
Password Certification: Gloria Sala (firstname.lastname@example.org)
Subjects: X-ray, Cataclysmic Variables, Nova
V5116 Sgr (=Nova Sgr 2005b), recently detected as a super-soft source with Swift (Ness et al. CBET #1030), was observed on 5 March 2007 by XMM-Newton, with a total exposure of 13 ks in the EPIC-MOS cameras and 9 ks in the EPIC-pn. The source count-rates in the EPIC cameras were 2-4 cts/s (MOS1 and MOS2) and 10-15 cts/s (pn) during most of the observation, increasing to 11-15 cts/s (MOS1 and MOS2) and 50-60 cts/s (pn) during 3.5 ks.
The high flux of the source caused pile-up in the three EPIC cameras. We therefore exclude the central pixels for spectral analysis. The spectrum of the source was very soft, with most of the emission below 0.7 keV, both in the EPIC cameras and in the RGSs. The EPIC-MOS spectra are poorly fit with an absorbed blackbody. A better fit is obtained with an ONe white dwarf atmosphere model (gently provided by J. MacDonald; MacDonald & Vennes, 1991, ApJ, 373, L51), with NH=1.3(+/-0.1)x1021cm-2 and T=6.1(+/-0.6)x105K. The luminosity determined from the normalization of the atmosphere model is L=4.8(+/-0.7)(d/10kpc)2x1036erg/s for the low rate spectra, and L=2.6(+/-0.7)(d/10kpc)2x1037erg/s for the high rate spectra. A CO white dwarf atmosphere model gives a worse fit. The ONe atmosphere model also fits reasonably well the RGS broad band spectra, but the residuals show a number of features that require a more detailed spectral modeling.