  We investigate the effects of inverse Compton scattering by electrons and
positrons in the unshocked winds of rotationally-powered binary pulsars. This
process can scatter low energy target photons to produce gamma rays with
energies from MeV to TeV. The binary radio pulsars PSR B1259-63 and PSR
J0045-73 are both in close eccentric orbits around bright main sequence stars
which provide a huge density of low energy target photons. The inverse Compton
scattering process transfers momentum from the pulsar wind to the scattered
photons, and therefore provides a drag which tends to decelerate the pulsar
wind. We present detailed calculations of the dynamics of a pulsar wind which
is undergoing inverse Compton scattering, showing that the deceleration of the
wind of PSR B1259-63 due to `inverse Compton drag' is small, but that this
process may confine the wind of PSR J0045-73 before it attains pressure balance
with the outflow of its companion star. We calculate the spectra and light
curves of the resulting inverse Compton emission from PSR B1259-63 and show
that if the size of the pulsar wind nebula is comparable to the binary
separation, then the gamma-ray emission from the unshocked wind may be
detectable by atmospheric Cerenkov detectors or by the new generation of
satellite-borne gamma-ray detectors such as INTEGRAL and GLAST. This mechanism
may therefore provide a direct probe of the freely-expanding regions of pulsar
winds, previously thought to be invisible.
