V5116 Sgr: a disc-eclipsed SSS post-outburst nova?

摘要

Nova V5116 Sgr 2005 No. 2, discovered on 2005 July 4, was observed withXMM-Newton in March 2007, 20 months after the optical outburst. The X-rayspectrum showed that the nova had evolved to a pure supersoft X-ray source,indicative of residual H-burning on top of the white dwarf. The X-raylight-curve shows abrupt decreases and increases of the flux by a factor 8 witha periodicity of 2.97h, consistent with the possible orbital period of thesystem. The EPIC spectra are well fit with an ONe white dwarf atmosphere model,with the same temperature both in the low and the high flux periods. This rulesout an intrinsic variation of the X-ray source as the origin of the fluxchanges, and points to a possible partial eclipse as the origin of the variablelight curve. The RGS high resolution spectra support this scenario showing anumber of emission features in the low flux state, which either disappear orchange into absorption features in the high flux state. A new XMM-Newtonobservation in March 2009 shows the SSS had turned off and V5116 Sgr hadevolved into a weaker and harder X-ray source.