  We show that the presence of a steady $\ao$ dynamo in astrophysical rotators
likely leads to an outflow of relative magnetic helicity and thus magnetic
energy available for particle acceleration in a corona. The connection between
energy and magnetic helicity arises because the generation of large scale field
is linked to a generation of large scale magnetic helicity. In a steady state,
the relative magnetic helicity associated with the large scale field can
escape, accompanied by an equal and opposite small scale contribution from the
field, since the total magnetic helicity in large magnetic Reynolds number
flows is conserved. From the helicity flow, a lower limit on the magnetic
energy deposited in the corona can be estimated. Steady coronal activity and
the dissipation of magnetic energy is therefore a signature of an internal
dynamo. Our theoretical estimate of the power delivered by a mean field dynamo
is consistent with that inferred from observations to be delivered to the solar
corona, the Galactic corona, and Seyfert I AGN coronae.
