Can gravitational waves be detected in quasar microlensing?

Studies of the lensed quasar $\mathrm{Q}0957+561\mathrm{A},\mathrm{B}$ have shown evidence for microlensing in the brightness history of the quasar images. It had been suggested that a frequency offset between the brightness fluctuations in each of the two images might possibly be caused by gravitational radiation generated by a massive black hole binary at the center of the lensing galaxy. This paper demonstrates that the fluctuations produced by such a source of gravitational waves will be too small to account for the observed frequency offsets.