  We consider the parabolic Anderson model (PAM) which is given by the equation
$\partial u/\partial t = \kappa\Delta u + \xi u$ with $u\colon\, \Z^d\times
[0,\infty)\to \R$, where $\kappa \in [0,\infty)$ is the diffusion constant,
$\Delta$ is the discrete Laplacian, and $\xi\colon\,\Z^d\times [0,\infty)\to\R$
is a space-time random environment that drives the equation. The solution of
this equation describes the evolution of a "reactant" $u$ under the influence
of a "catalyst" $\xi$. In the present paper we focus on the case where $\xi$ is
a system of $n$ independent simple random walks each with step rate $2d\rho$
and starting from the origin. We study the \emph{annealed} Lyapunov exponents,
i.e., the exponential growth rates of the successive moments of $u$ w.r.t.\
$\xi$ and show that these exponents, as a function of the diffusion constant
$\kappa$ and the rate constant $\rho$, behave differently depending on the
dimension $d$. In particular, we give a description of the intermittent
behavior of the system in terms of the annealed Lyapunov exponents, depicting
how the total mass of $u$ concentrates as $t\to\infty$. Our results are both a
generalization and an extension of the work of G\"artner and Heydenreich 2006,
where only the case $n=1$ was investigated.
