  Through detailed numerical simulations, we demonstrate that relativistic
outflows (Lorentz factor $\Gamma \sim 7$) of electron-positron pairs can be
produced by radiative acceleration even when the flow starts from a nearly pair
equilibrium state at subrelativistic temperatures. Contrary to the expectation
that pairs annihilate during an expansion stage for such low temperatures, we
find that most pairs can survive for the situations obtained in our previous
work. This is because in the outflow-generating region the dynamical timescale
is short enough even though the fireball is optically thick to scattering.
Several problems that should be solved to apply to actual active galactic
nucleus jets are discussed.
