Evidence for a Very Slow X‐Ray Pulsar in 2S 0114+650 fromRossi X‐Ray Timing ExplorerAll‐Sky Monitor Observations

Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) observations of theX-ray binary 2S0114+650 show modulations at periods close to both the opticallyderived orbital period (11.591 days) and proposed pulse period (~ 2.7 hr). Thepulse period shows frequency and intensity variability during the more than 2years of ASM observations analyzed. The pulse properties are consistent withthis arising from accretion onto a rotating neutron star and this would be theslowest such period known. The shape of the orbital light curve showsmodulation over the course of the entire orbit and a comparison is made withthe orbital light curve of Vela X-1. However, the expected phase of eclipse,based on an extrapolation of the optical ephemeris, does not correspond withthe observed orbital minimum. The orbital period derived from the ASM lightcurve is also slightly longer than the optical period.Comment: To be published in the Astrophysical Journal, 1999, volume 511. 9 figure