  We consider a graphene sheet in the presence of a strong perpendicular
magnetic field with a single short-range delta-impurity situated at one of the
carbon sites. We study the neutral inter-Landau level collective excitations,
magnetoplasmons, which become localized on the impurity. Some of these
excitations involve a pseudospin flip (intervalley transitions), since the
impurity can scatter electrons between the two valleys. We propose a
classification of states of the excitations in graphene and introduce the
appropriate quantum numbers. The energies and optical strengths of collective
excitations are calculated for a range of integer filling factors and impurity
strengths. We establish a set of symmetries matching the energies and
absorption strengths of collective excitations for different sublattice
locations of the impurity, filling factors, circular light polarizations and
signs of the impurity potential.
