  Superstring field theory was recently used to derive a four-dimensional
Maxwell action with manifest duality. This action is related to the
McClain-Wu-Yu Hamiltonian and can be locally coupled to electric and magnetic
sources.
  In this letter, the manifestly dual Maxwell action is supersymmetrized using
N=1 and N=2 superspace. The N=2 version may be useful for studying
Seiberg-Witten duality.
