  We calculate the properties of gamma-ray burst spectral lines formed by
resonant cyclotron scattering in a radiation-driven outflow. Most previous
models of line formation in gamma-ray bursts are appropriate at the polar cap
of a neutron star located no further than several hundred parsecs away.
However, the BATSE brightness and sky distributions indicate that, if bursters
are galactic, they are located in a corona at distances greater than 100 kpc.
At these distances the burst luminosity exceeds the Eddington luminosity and
the plasma in a polar line-forming region is ejected along the field lines. The
variation of the magnetic field strength and plasma velocity with altitude in
such an outflow would seem to prevent the formation of narrow features like
those observed by Ginga and other instruments. However, this is not the case
because the majority of scatters occur close to the stellar surface, at
altitudes below $z \approx r_h$, where $r_h \sim 10^{5}$ cm is the size of the
photon source. Consequently, the interpretation of the observed features as
cyclotron lines does not rule out burst sources in a galactic corona. The
outflow model predicts both absorption-like and single-peaked emission-like
features. The latter do not occur in models with static line-forming regions,
but have been observed in gamma-ray bursts by the Konus and BATSE instruments.
