(a) Timing analysis plots for the Swift/XRT observations. The top panel shows the 0.3–10 keV light curve. The bottom left panel shows the photon arrival time (solid line) vs. the expectation for a constant count rate (dashed line), used to calculate the K-S probability of non-variability. (b) The bottom right panel shows the 3–200 mHz periodogram, used to calculate F_var (see the text for details).