  Unlike in the Schwarzschild black hole background, gravitational
perturbations in a Kerr black hole background can not be decomposed into simple
tensor harmonics in the time domain. Here, we make mode decompositions only in
the azimuthal direction. As a first step, we discuss the resulting
(2+1)-dimensional Klein-Gordon differential equation for scalar perturbations
with a two dimensional Dirac's $\delta$-function as a source representing a
point particle orbiting a much larger black hole. To make this equation
amenable for numerical integrations we explicitly remove analytically the
singular behavior of the source and compute a global, well bahaved, effective
source for the corresponding waveform.
