R_C-band light curves of all (long) afterglows in the sample of Kann et al. (2010, 2011); some extraordinary bright events are indicated. All data have been corrected for Galactic extinction. Triangles indicate equivalent R_C-band upper limits of the afterglows in our sample (Table 2). The blue dashed/dotted line approximately indicates the mean of the afterglow brightness distribution. The red straight line, 1.5 mag below the blue line, indicates the border line of all targets in our study. A colour version of the figure is available in the electronic version.