Using the exceptional monitoring capabilities of the MACHO project we present here the optical history of the LMC supersoft source ( SSS ) RX J0513.9-6951 , for a continuous 3 year period .
Recurring low states , in which the optical brightness drops by up to a magnitude , are observed at quasi-regular intervals .
This provides a crucial insight into the nature of the SSS and , in particular , a chance to investigate the poorly understood behaviour of their accretion discs .
Analysis of the high state data reveals a small modulation of semi-amplitude \sim 0.02 magnitudes at P = 0.76278 \pm 0.00005 days , a period which is consistent with the current “ best ” suggested spectroscopic value .