  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.
