* Astronomy

Title: A Detailed Study of 2S 0114+650 with the RXTE
Authors: S. A. Farrell, R. K. Sood, P. M. O'Neill, S. Dieters

We present the results of a detailed study of the high mass X-ray binary 2S 0114+650 made with the pointed instruments onboard the Rossi X-ray Timing Explorer. The spectral and temporal behaviour of this source was examined over the pulse, orbital, and super-orbital timescales, covering 2 cycles of the 30.7 d super-orbital modulation. Marginal evidence for variability of the power law photon index over the pulse period was identified, similar to that observed from other X-ray pulsars. If this variability is real it could be attributed to a varying viewing geometry of the accretion region with the spin of the neutron star. Variability of the neutral hydrogen column density over the orbital period was observed, which we attribute to the line of sight motion of the neutron star through the dense circumstellar environment. A hardening of the spectrum was observed during the orbital maximum, which we attribute to absorption effects as the neutron star undergoes partial eclipse. No significant variability of the column density was observed over the super-orbital period, indicating that variable obscuration by a precessing warp in an accretion disc is not the mechanism behind the super-orbital modulation. In contrast, a significant softening of the spectrum was observed during the super-orbital minimum. We conclude that the observed super-orbital modulation is tied to variability in the mass accretion rate due to some as yet unidentified mechanism.

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