Published online by Cambridge University Press: 20 November 2018
We consider Tate cycles on an Abelian variety $A$ defined over a sufficiently large number field $K$ and having complexmultiplication. We show that there is an effective bound $C\,=\,C(A,\,K)$ so that to check whether a given cohomology class is a Tate class on $A$, it suffices to check the action of Frobenius elements at primes $v$ of norm $\le \,C$. We also show that for a set of primes $v$ of $K$ of density 1, the space of Tate cycles on the special fibre ${{A}_{v}}$ of the Néron model of $A$ is isomorphic to the space of Tate cycles on $A$ itself.