  Rossby waves (or r-modes) on the surface of a neutron star have become a
leading model for the oscillations observed during the tail of Type-I X-ray
bursts. Their frequency evolution matches well with the observed frequency
drifts of the oscillations in the bursts, and the burning appears to excite
these waves quite naturally. This paper addresses the detailed shape of the
expected flux profiles from r-modes on neutron stars as a function of energy.
R-modes naturally account for both the small amplitude of the observed
oscillations and their lack of harmonic content. However, the model predicts
that the oscillation at higher energies leads the lower energy variation. The
observed oscillations have the opposite trend which possibly indicates that the
higher energy photons are upscattered in the plasma surrounding the neutron
star and therefore delayed.
