SIMBAD references

We have obtained high time resolution (seconds) photometry of LMC X-2 in 1997 December, simultaneously with the Rossi X-ray Timing Explorer (RXTE), in order to search for correlated X-ray and optical variability on time-scales from seconds to hours. We find that the optical and X-ray data are correlated only when the source is in a high, active X-ray state. Our analysis shows evidence for the X-ray emission leading the optical with a mean delay of <20 s. The time-scale for the lag can be reconciled with disc reprocessing, driven by the higher-energy X-rays, only by considering the lower limit for the delay. The results are compared with a similar analysis of archival data of Sco X-1.