Concatenated Chandra observations of VFTS 399 (975 ks combined exposure). Binned flux and associated 1σ errors are shown in black, while binned median energies are shown in red. A sliding-window lightcurve inferred from the individual events (i.e. no binning) is shown by the blue lines, with a 68% pointwise confidence band limit represented by the two lines. Running left to right, the start dates of the 20 epochs of observations are given in Table 3.