RXTE OBSERVATIONS OF THE BE STAR X-RAY TRANSIENT X0726-260 (4U-0728-25) - ORBITAL AND PULSE PERIODS

Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor observations of the transient Be star X-ray source X0726-260 suggest a 34.5 day period. T his is apparently confirmed by a serendipitous RXTE Proportional Count er Array (PCA) slew detection of the source on 1997 May 5, near the ti me of a predicted flux maximum. A subsequent 5 ks pointed observation of X0726-260 with the RXTE PCA detector was carried out on 1997 June 7 , when X0726-260 was predicted to be bright again, and this revealed p ulsations at a period of 103.2 s. If the 34.5 day period is orbital, t hen the pulse period is surprisingly long compared with that predicted by the correlation between orbital period and spin period observed fo r other Be/neutron star systems. A possible similarity with GRO J205842 is briefly discussed.