A New Clue to the Transition Mechanism between Optical High and Low States of the Supersoft X-ray Source Rx J0513.9−6951, Implied from the Recurrent Nova Ci Aquilae 2000 Outburst Model

We have found a new clue to the transition mechanism between optical high/X-ray off and optical low/X-ray on states of the LMC supersoft X-ray source RX J0513.9−6951. A sharp ∼ 1 mag drop is common to the CI Aql 2000 outburst. These drops are naturally attributed to cessation of optically thick winds on white dwarfs. A detailed light-curve analysis of CI Aql indicates that the size of a disk drastically shrinks when the wind stops. This causes ∼ 1− 2 mag drop in the optical light curve. In RX J0513.9−6951, the same mechanism reproduces sharp ∼ 1 mag drop from optical high to low states. We predict this mechanism also works on the transition from low to high states. Interaction between the wind and the companion star attenuates the mass transfer and drives full cycles of low and high states. Subject headings: binaries: close — novae, cataclysmic variables — stars: individual (CI Aquilae, RX J0513.9−6951) — stars: winds, outflows — X-rays: stars