The Low Luminosity Transient Pulsar SAX J2103.5+4545

The 1999 outburst of the transient pulsar SAX J2103.5+4545 was monitored withRXTE until the pulsar faded below 1 mCrab. The 358 s pulsar was spun up for 150days. Then the flux dropped quickly, the frequency saturated and as the fluxcontinued to decline a weak spindown began, with pulses remaining strong. XMMNewton EPIC observations in quiescence would determine the quiescent level andthe nature of the flux, pulsations, and spectra after outburst decay.Observations finding the source in outburst would measure spectral correlationswith the transient.s evolution and with the phase of the 12.68 day eccentricorbit. These measurements would be diagnostic of the nature of the mass loss ofthe companion and the interaction of a strong field pulsar with the wind. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]