  Unitary limit for model point scatterers in graphene is known to reveal
low-energy resonances. The same limit could be achieved from hybridization of
band electrons with the localized impurity level positioned in the vicinity of
the Fermi level. The finite size defects represent an easier realization of the
effective unitary limit, occurring when the Fermi wavelength induced by the
potential becomes of the order of the size of the defect. We calculate the
induced electron density and find two signatures of a strong impurity,
independent of its specific realization. The dependence of the impurity-induced
electron density on the distance changes near resonances from ~r^{-3} to
~r^{-2}. The total number of induced particles at the resonance is equal to one
per degree of spin and valley degeneracy. The effects of doping on the induced
density are found.
