  Using the 2.4m MDM and 8.4m Large Binocular Telescope, we observed nine GRB
afterglows to systematically probe the late time behaviors of afterglows
including jet breaks, flares, and supernova bumps. In particular, the LBT
observations have typical flux limits of 25-26 mag in the Sloan r' band, which
allows us to extend the temporal baseline for measuring jet breaks by another
decade in time scale. We detected four jet breaks (including a "textbook" jet
break in GRB070125) and a fifth candidate, all of which are not detectable
without deep, late time optical observations. In the other four cases, we do
not detect the jet breaks either because of contamination from the host galaxy
light, the presence of a supernova bump, or the intrinsic faintness of the
optical afterglow. This suggests that the basic picture that GRBs are
collimated is still valid and that the apparent lack of Swift jet breaks is due
to poorly sampled afterglow light curves, particularly at late times. Besides
the jet breaks, we also detected late time flares, which could attribute to
late central engine activities, and two supernova bumps.
