  Oscillations in the X-ray flux of thermonuclear X-ray bursts have been
observed with RXTE from at least 6 low-mass binaries, at frequencies from 330
Hz to 589 Hz. There appear to be preferred relations between the frequencies
present during the bursts and those seen in the persistent flux. The amplitude
of the oscillations can exceed 50 % near burst onset. Except for a systematic
increase in oscillation frequency as the burst progresses, the frequency is
stable. Time resolved spectra track increases in the X-ray emitting area due to
propagation of the burning front over the neutron star surface, as well as
radiation driven expansion of the photosphere. The neutron star mass, radius,
and distance can be inferred when spectra are compared to theoretical
expectations.
