Optical variability of the Large Magellanic Cloud supersoft source RX J0513.9 - 6951 from MACHO Project photometry

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 supersoft sources 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 ∼ 0.02 mag at P=0.762 78 ±0.000 05 d, a period which is consistent with the current 'best' suggested spectroscopic value.