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D. Chakrabarty, E. H. Morgan (MIT), R. Wijnands (St. Andrews), M. van der Klis (Amsterdam), D. K. Galloway, M. P. Muno (MIT), C. B. Markwardt (NASA/GSFC and Maryland)
Four thermonuclear X-ray bursts showing photospheric radius expansion were detected in 2002 October from the milisecond X-ray pulsar SAX J1808.4-3658, and 401 Hz millisecond oscillations were detected during each of these bursts. The oscillation frequency in the burst tails was stationary and identical to the spin frequency as determined from persistent X-ray pulsations in the non-burst emission, while the oscillation in the burst rise showed evidence for either a very rapid 2-3 Hz drift or a pair of simultaneous pulsations. These observations verify the identification of thermonuclear burst oscillations with the neutron star spin frequency. We discuss the phase relationship of the burst oscilations and the persistent pulsations, and the implications of these observations for the population of millisecond pulsars.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.