Characteristic L_X vs. stellar mass for WTTSs and CTTSs (left and right panels, respectively). The samples are selected in the same way as for our variability study except that in this case we did not impose an X-ray flux (or count-rate) limit. Filled circles refer to the count-rate-limited sample used for the variability study. Linear fits are computed from all points (both filled and empty symbols) within the x-axis range spanned by the gray lines that represent them.