Abstract
Recent Swift X-ray monitoring campaigns of novae have revealed extreme levels of variability during the early super-softsource (SSS) phase. The first time this was observed was during the 2006 outburst of the recurrent nova RS Oph which was also extensively covered by grating observations with XMM-Newton and Chandra. I focus here on an XMM-Newton observation taken on day 26.1, just before Swift confirmed the start of the SSS phase, and a Chandra observation taken on day 39.7. The first observation probes the evolution of the shock emission produced by the collision of the nova ejecta with the stellar wind of the companion. The second observation contains bright SSS emission longwards of 15°A while at short wavelengths, the shock component can be seen to have hardly changed. On top of the SSS continuum, additional emission lines are clearly seen, and I show that they are much stronger than those seen on day 26.1, indicating line pumping caused by the SSS emission. The lightcurve on day 39.7 is highly variable on short time scales while the long-term Swift light curve was still variable. In 2007, we have shown that brightness variations are followed by hardness variations, lagging behind 1000 seconds. I show now that the hardness variations are owed to variations in the depth of the neutral hydrogen column density of order 25%, particularly affecting the oxygen K-shell ionization edge at 0.5 keV.
Highlights
The 2006 outburst of the recurrent symbiotic nova RS Oph has attracted a large number of observers to study the outburst in unprecedented detail and many wavelength bands
I focus here on an XMM-Newton observation taken on day 26.1, just before Swift confirmed the start of the SSS phase, and a Chandra observation taken on day 39.7
On top of the SSS continuum, additional emission lines are clearly seen, and I show that they are much stronger than those seen on day 26.1, indicating line pumping caused by the SSS emission
Summary
The 2006 outburst of the recurrent symbiotic nova RS Oph has attracted a large number of observers to study the outburst in unprecedented detail and many wavelength bands. Between days ∼ 30 and 45, the X-ray count rate was highly variable between ∼ 10 counts per second (cps) and 200 cps, and stabilized at ∼ 300 cps (figure 2 in Osborne et al 2011) This was a new discovery and was later observed in other novae and might be a general phenomenon. The line profiles contained clear signs of emission lines in the red wings (figure 5 of Ness et al 2007) which could either come from residual shock emission or are part of P Cyg profiles During this observation, the nova was highly variably on shorter time scales, and Ness et al (2007) reported that the hardness variations followed the same up- and down trends but lagged 1000 seconds behind (see Fig. 1). Modeling shows that the overall column density increases with decreasing brightness (Sect. 2.2)
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