A note on gravitational wave lensing

In a recent paper [Ruffa] it was proposed that the massive black hole at the Galactic center may act as a gravitational lens focusing gravitational wave energy to the Earth. Considering the gravitational wave signal emitted by galactic spinning pulsars, an enhancement in the gravitational wave intensity by a factor of a few thousand is found. For galactic and extra-galactic sources the intensity enhancement can be as high as 4,000 and 17,000, respectively. In this note we consider the probability of significant signal enhancement from galactic and extra-galactic pulsars by the proposed mechanism and find that it is actually negligible. The lensing effect due to a possible companion object (a star or the galactic center black hole) of the gravitational wave source is also investigated in the framework of the classical microlensing theory.