SAX J1808.4-3658
From Wikipedia, the free encyclopedia
A transient X-ray source first discovered in 1996 by the Italian BeppoSAX satellite, SAX J1808.4-3658 revealed X-ray pulsations at the 401 Hz neutron star spin frequency when it was observed during a subsequent outburst in 1998 by NASA's RXTE satellite. The neutron star orbits a brown dwarf binary companion every 2.01 hours. X-ray burst oscillations and quasi-periodic oscillations in addition to coherent X-ray pulsations have been seen from SAX J1808.4-3658, making it a Rosetta stone for interpretation of the timing behavior of low-mass X-ray binaries.
These accreting millisecond X-ray pulsars are thought to be the evolutionary progenitors of recycled radio millisecond pulsars. A total of seven accreting millisecond X-ray pulsars have been discovered as of October 2006.