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C. B. Markwardt (U. Maryland & NASA/GSFC)
Millisecond X-ray pulsars are faint X-ray transient systems with low duty cycles. They are active for only a few weeks after quiescence periods of several years. Mass transfer rates -- presumably driven in part by gravitational radiation -- are low enough that the X-ray outbursts are typically quite faint and difficult to detect with all-sky monitoring approaches. After the discovery of the first X-ray pulsar, SAX J1808.4-3658, dedicated high-sensitivity RXTE PCA monitoring programs have been successful in discovering several more millisecond pulsar systems, in addition to new outbursts of the original. The discovery of new millisecond pulsar systems reveals information about the distributions of orbital periods and companion sizes. Continued monitoring of known sources will eventually yield their outburst recurrence periods, and hence the time-averaged accretion rates. Spin rate changes during the outburst itself indicate the instantaneous accretion rate. Thus, accreting millisecond X-ray pulsars truly provide a laboratory for the study of accretion physics.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.