Some dynamical systems possess invariant submanifolds such that the dy
namics restricted to the invariant submanifold is chaotic. This situat
ion arises in systems with a spatial symmetry or in the synchronizatio
n of chaotic oscillators. The invariant submanifold could become unsta
ble to perturbations in the transverse directions when a parameter of
the system is changed through a critical blow-our value. This could re
sult in an extreme form of temporally intermittent bursting called on-
off intermittency. We propose a model that incorporates the universal
features of systems that display on-off intermittency. We study this m
odel both with and without additive noise and we derive scaling result
s for the power spectral density of the on-off intermittent process an
d for the box counting dimension for the set of time intervals when th
e process takes on values above a given threshold. We then present num
erical simulations realizing these results.