Prediction of Supersoft X-ray Phase during the 2006 Outburst of RS Ophiuchi

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