  We present observations of the 9.8 s X-ray pulsar XTE J1859+083 made with the
ASM and PCA on board RXTE, and the WFC on board BeppoSAX. The ASM data cover a
12 year time interval and show that an extended outburst occurred between
approximately MJD 50,250 and 50,460 (1996 June 16 to 1997 January 12). The ASM
data excluding this outburst interval suggest a possible modulation with a
period of 60.65 +/- 0.08 days. Eighteen sets of PCA observations were obtained
over an approximately one month interval in 1999. The flux variability measured
with the PCA appears consistent with the possible period found with the ASM.
The PCA measurements of the pulse period showed it to decrease
non-monotonically and then to increase significantly. Doppler shifts due to
orbital motion rather than accretion torques appear to be better able to
explain the pulse period changes. Observations with the WFC during the extended
outburst give a position which is consistent with a previously determined PCA
error box, but which has a significantly smaller error. The transient nature of
XTE J1859+083 and the length of its pulse period are consistent with it being a
Be/neutron star binary. The possible 60.65 day orbital period would be of the
expected length for a Be star system with a 9.8 s pulse period.
