  It was pointed out by Paczynski (1987) that the X-ray luminosity of accreting
neutron stars is very sensitive to the physical properties of the accretion
flow close to the innermost stable circular orbit. The X-ray radiation is
dominated by that emitted in the boundary layer, where accreted matter hits a
star surface. The X-ray luminosity of the boundary layer is proportional to the
local accretion rate. In this note, we estimate local accretion rate variations
from the disk that undergoes non-stationary axisymmetric perturbations. The
perturbations are given by the poloidal-velocity potential. We obtain a simple
formula describing the modulation of the accretion rate for the particular case
of global vertical disk oscillations that have been recently studied by
Abramowicz et al. (2005).
