Multi-color observations of short GRB afterglows: 20 events observed
  between 2007 and 2010
  We report on follow-up observations of 20 short-duration gamma-ray bursts
performed in g'r'i'z'JHKs with the seven-channel imager GROND between mid-2007
and the end of 2010. This is one of the most comprehensive data sets on GRB
afterglow observations of short bursts published so far. In three cases GROND
was on target within less than 10 min after the trigger, leading to the
discovery of the afterglow of GRB 081226A and its faint underlying host galaxy.
In addition, GROND was able to image the optical afterglow and follow the
light-curve evolution in further five cases, GRBs 090305, 090426, 090510,
090927, and 100117A. In all other cases optical/NIR upper limits can be
provided on the afterglow magnitudes.
