  A new X-ray source, XTE J1855-026, was discovered during RXTE scans along the
galactic plane. The source shows pulsations at a period of 361 s and also
modulation at a period of 6.1 days which we interpret as the orbital period of
the system. The X-ray spectrum above ~3 keV can be fitted with an absorbed
power law model with a high-energy cut-off, and an iron emission line at
approximately 6.4 keV. We interpret these results as indicating that XTE
J1855-026 is likely to consist of a neutron star accreting from the wind of an
O or B supergiant primary. A less likely interpretation is that XTE J1855-026
is instead a Be/neutron star binary, in which case it would have the shortest
known orbital period for such a system.
