Rossi X‐Ray Timing ExplorerObservations of the X‐Ray Pulsar EXO 1722−363: A Candidate Eclipsing Supergiant System

Observations made of the X-ray pulsar EXO 1722-363 using the Proportional Counter Array (PCA) and the All-Sky Monitor (ASM) on board the Rossi X-Ray Timing Explorer ( RXTE ) reveal the orbital period of this system to be 9.741 ± 0.004 days from periodic changes in the source flux. The detection of eclipses together with the values of the pulse and orbital periods suggests that this source consists of a neutron star accreting from the stellar wind of an early spectral type supergiant companion. Pulse timing measurements were also obtained but do not strongly constrain the system parameters. The X-ray spectra can be well fitted with a model consisting of a power law with a high-energy cutoff and, for some spectra, a blackbody component with a temperature of approximately 0.85 keV.