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E. H. Morgan, D. Chakrabarty (MIT), R. Wijnands (St. Andrews), M. van der Klis (Amsterdam), C. Markwardt (GSFC and Maryland)
We report on pulse timing of the millisecond X-ray pulsar SAX J1808.4-3658 during its 2002 outburst with RXTE. The pulsar was spinning down at a constant rate over the outburst, despite a large dynamic range of X-ray flux over this time. The measured magnitude of the spin frequency derivative exceeds the maximum value expected from accretion torques by a factor of 5. The timing history also contains a small glitch with a very rapid recovery time scale. There was no evidence for a ~200 Hz pulsation subharmonic in the data, favoring our interpretation of 400.97521 Hz as the pulsar spin frequency. We compare these results with the spin and orbital elements derived in the 1998 and 2000 outburst of the source.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.