We consider planar massless scalar waves impinging upon a Kerr black hole,
for general angles of incidence. We compute the absorption cross section via
the partial wave approach, and present a gallery of results. In the
low-frequency regime, we show that the cross section approaches the horizon
area; in the high-frequency regime, we show that the cross section approaches
the geodesic capture cross section. In the aligned case, we extend the complex
angular momentum method to obtain a `sinc' approximation, which relates the
regular high-frequency oscillations in the cross section to the properties of
the polar null orbit. In the non-aligned case, we show, via a semi-analytic
approximation, that the reduction in symmetry generates a richer, less regular
absorption cross section. We separate the absorption cross section into
corotating and counterrotating contributions, showing that the absorption is
larger for counterrotating waves, as expected.Comment: 11 pages, 10 figure