Histogram (red; left Y axis) and cumulative (black; right Y axis) distributions of the exposure time of the 5303 Chandra observations used in this work. The inset provides a zoomed-in view to show the high-exposure-time tail of the distribution. The vertical dashed blue line indicates the median exposure time (=32 ks) of the total sample. We adopt an exposure time of 8 ks as a lower bound due to the strongly decreasing probability of distinguishing FXRTs in short exposures.