RS Ophiuchi is one of the well-observed recurrent novae and also a candidate progenitor of Type la supernovae. Its sixth recorded outburst was discovered on 2006 February 12. Detection of a supersoft X-ray phase will provide us with a firm confirmation of hydrogen shell burning on the white dwarf, and its turn-on/turnoff dates strongly constrain the mass range of the white dwarf, which will clarify whether or not RS Oph becomes a Type Ia supernova. For a timely detection of its supersoft X-ray phase, we have calculated the outburst evolution of RS Oph based on the optically thick wind theory and have predicted a supersoft X-ray phase for the 2006 outburst: it will most probably start between day 80 and day 90 and continue until days 110-120 after the optical maximum. Its duration is so short, only a month or so. We strongly recommend multiple observations during April, May, and June of 2006 to detect the turn-on and turnoff times of the supersoft X-ray phase.
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