Many thermonuclear X-ray bursts exhibit brightness oscillations. The
brightness oscillations are thought to be due to the combined effects of
non-uniform nuclear burning and rotation of the neutron star. The waveforms of
the oscillations contain information about the size and number of burning
regions. They also contain substantial information about the mass and radius of
the star, and hence about strong gravity and the equation of state of matter at
supranuclear densities. We have written general relativistic ray-tracing codes
that compute the waveforms and spectra of rotating hot spots as a function of
photon energy. Using these codes, we survey the effect on the oscillation
waveform and amplitude of parameters such as the compactness of the star, the
spot size, the surface rotation velocity, and whether there are one or two
spots. We also fit phase lag versus photon energy curves to data from the
millisecond X-ray pulsar, SAX J1808--3658.Comment: To appear in Proc. of the 10th Annual October Astrophysics Conference
in Maryland: Cosmic Explosions, 4 page
