THE PERIODS DISCOVERED BY RXTE IN THERMONUCLEAR FLASH BURSTS

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 persis tent flux. The amplitude of the oscillations can exceed 50 % near burs t onset. Except for a systematic increase in oscillation frequency as the burst progresses, the frequency is stable. Time resolved spectra t rack increases in the X-ray emitting area due to propagation of the bu rning front over the neutron star surface, as well as radiation driven expansion of the photosphere. The neutron star mass, radius, and dist ance can be inferred when spectra are compared to theoretical expectat ions.