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

TL;DR

This study observes V5116 Sgr 20 months post-outburst, revealing a supersoft X-ray source with flux variability likely caused by partial eclipses, and notes its evolution into a weaker, harder X-ray source over two years.

Contribution

It provides the first detailed X-ray spectral and timing analysis of V5116 Sgr post-outburst, suggesting partial eclipses as the cause of flux variability and tracking its evolution into a weaker X-ray source.

Findings

Flux varies by a factor of 8 with a 2.97h period.

Spectral analysis supports partial eclipse scenario.

The supersoft source turned off after two years.

Abstract

Nova V5116 Sgr 2005 No. 2, discovered on 2005 July 4, was observed with XMM-Newton in March 2007, 20 months after the optical outburst. The X-ray spectrum 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-ray light-curve shows abrupt decreases and increases of the flux by a factor 8 with a periodicity of 2.97h, consistent with the possible orbital period of the system. 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 rules out an intrinsic variation of the X-ray source as the origin of the flux changes, and points to a possible partial eclipse as the origin of the variable light curve. The RGS high resolution spectra support this scenario showing a number of emission features in the low flux state, which either disappear or change into absorption features in the high flux state. A new XMM-Newton observation in March 2009 shows the SSS had turned off and V5116 Sgr had evolved into a weaker and harder X-ray source.