  In 1996 during Rossi X-ray Timing Explorer (RXTE) observations of SGR
1900+14, the 89-s X-ray pulsar XTE J1906+09 was discovered. As a result of
monitoring campaigns of SGR 1900+14, XTE J1906+09 was also monitored regularly
in 1996 September, 1998 May-June, 1998 August-1999 July, and 2000 March-2001
January. A search for pulsations in these observations resulted in detections
of only the two previously reported outbursts in 1996 September and 1998
August- September. Pulsed flux upper limits for the remaining observations
indicate that XTE J1906+09 is a transient X-ray pulsar and therefore likely has
a Be star companion. XTE J1906+09 was not detected with the RXTE All Sky
Monitor. Pulse timing analysis of the second outburst revealed a sinusoidal
signature in the pulse frequencies that is likely produced by periastron
passage in an orbit. Fits to pulse phases using an orbital model and quadratic
phase model have chi^2 minima at orbital periods of 26-30 days for fixed mass
functions of 5, 10, 15, and 20 M_sun. The pulse shape showed intensity and
energy dependent variations. Pulse phase spectroscopy was used to quantify the
energy dependent variations. The phase averaged spectrum, using the pulse
minimum spectrum as the background spectrum to eliminate effects from SGR
1900+14 and the galactic ridge, was well fitted by an absorbed power law with a
high energy cutoff. Estimated 2-10 keV peak fluxes, corrected for contributions
from the galactic ridge and SGR 1900+14, are 6E-12 ergs/cm^2/s and 1.1E-10
ergs/cm^2/s for the 1996 and 1998 outbursts, respectively. XTE J1906+09 may be
a member of an unusual class of Be/X-ray binaries that do not lie on the
general spin period versus orbital period correlation with the majority of
Be/X-ray binaries.
