  We consider a gravitational plane wave passing through a galactic dark matter
halo composed of weakly self-interacting, self-gravitating, Bose-Einstein
condensate of ultralight particles. Treating the gravitational wave as a time
dependent perturbation, we study energy transfer between the gravitational wave
and the Bose-Einstein condensate by applying linear response theory to a
non-uniform condensate described by the Bogoliubov-de Gennes theory, and
compute the fractional loss in gravitational wave energy. We apply our results
to investigate the extent to which this loss effects the estimation of the
distance between the gravitational wave source and the earth. We show that the
effect is negligible.
