X-ray variability in the Chandra Deep Field South

We present the preliminary results of an X-ray variability study of sources detected in the Chandra Deep Field South (Giacconi et al. 2002). We both investigate the long-term variability, binning the lightcurves in order to achieve the maximum S/N ratio for faint sources, and analyze the short-term variability of stronger sources. We found that the fraction of variable objects increases with total counts, consistent with the better statistics. To validate our quantitative analysis we perform extensive simulations mimicking the observing conditions for each source. We use our simulations to predict the fraction of sources which are variable. We will quantify the variable flux fraction, and the dependence of variability on several physical parameters.