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Session 113 - Old Worn-Out Stars.
Oral session, Thursday, January 16
Piers 2/3,
The proportional counter array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) is capable of detecting kilohertz oscillations with amplitudes as small as 1 - 2 Type I X-ray bursts. We report on the detection of millisecond oscillations during bursts from two different sources, the "slow burster" 4U1728-34 and an as yet unidentified source in the Galactic center region. The oscillations have frequencies of 363 and 589 Hz respectively. They are not strictly coherent, particularly during the rise and near-peak portions of the bursts, with widths of 1 to 1.5 Hz. However, in both sources the oscillations become effectively coherent as the bursts decay. We argue that stellar rotation is the most likely cause of the oscillations and discuss the results in terms of this interpretation and its implications for the origins of millisecond pulsars.
