Optical variability of the LMC 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 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 mag at $P=$0.76278$\pm$0.00005~d, a period which is consistent with the current ``best’’ suggested spectroscopic value.