  We present real-time detection measurements of electron tunneling in a
graphene quantum dot. By counting single electron charging events on the dot,
the tunneling process in a graphene constriction and the role of localized
states are studied in detail. In the regime of low charge detector bias we see
only a single time-dependent process in the tunneling rate which can be modeled
using a Fermi-broadened energy distribution of the carriers in the lead. We
find a non-monotonic gate dependence of the tunneling coupling attributed to
the formation of localized states in the constriction. Increasing the detector
bias above 2 mV results in an increase of the dot-lead transition rate related
to back-action of the charge detector current on the dot.
