The optical long ‘period’ of LMC X-3

We have studied the long-term variability of LMC X-3 in optical light curves spanning 6 yr, in order to search for optical signatures which could confirm or refute the suggestion that the ‘modulation’ is the result of accretion-rate variability rather than accretion-disc precession. We find that there is no stable period in the optical light curves, that the optical and X-ray light curves are correlated, with an X-ray lag, and that there is no modulation in the optical colours. We argue that these effects agree with the variable mass-accretion rate model proposed by Wilms et al.