  A dispersive representation based on unitarity and analyticity is used to
study the low energy $\gamma N \to \pi N\ \text{and}\ \gamma^* N \to \pi N$
partial wave amplitudes. Final state interactions of the $\pi N$ system are
critical to this analysis. The left-hand cut contribution is estimated by
invoking baryon chiral perturbation theory results, while the right-hand cut
contribution responsible for final state interaction effects is taken into
account via an Omn\`{e}s formalism with elastic phase shifts as input. It is
found that a good numerical fit can be achieved with only one subtraction
parameter, and the experimental data of the multipole amplitudes $E_{0+},
S_{0+}$ in the energy region below the $\Delta (1232)$ are well described when
the photon virtuality $Q^2 \leq 0.1 \mathrm{GeV}^2$. Furthermore, we extend the
partial wave amplitudes to the second Riemann sheet to extract the couplings of
the subthreshold resonance $N^*(890)$. Its couplings extracted from the
multipole amplitudes $E_{0+}, S_{0+}$ are comparable to those of the $N^*
(1535)$ resonance.
