  We consider the inverse problem of determining the time and space dependent
electromagnetic potential of the Schr\"odinger equation in a bounded domain of
$\mathbb R^n$, $n\geq 2$, by boundary observation of the solution over the
entire time span. Assuming that the divergence of the magnetic potential is
fixed, we prove that the electric potential and the magnetic potential can be
H\"older stably retrieved from these data, whereas stability estimates for
inverse time-dependent coefficients problems of evolution partial differential
equations are usually of logarithmic type.
