Luminosity evolution of the X-ray afterglows of the short bursts in our sample. Highlighted are the bursts with optical afterglows (Figs. 14, 15). Black lines represent the afterglows of the likely Type II events GRB 090426 and GRB 00927, green the afterglows of the Type I events GRBs 081226A, 090510, and 100117A. No X-ray afterglow light curve was reported for GRB 090305. Overplotted is also the short-burst sample compiled by Kann et al. (2011) (red color) as well as the X-ray afterglows of the long-burst sample with known redshift (gray). All short-burst afterglows are less luminous than the mean of long-burst afterglow luminosities (orange line); however, there is a continuous overlap between short and long GRB afterglows.