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 can 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 reduction in
the power law photon index was observed during the orbital maximum, which we
speculate is due to absorption effects as the neutron star passes behind a
heavily absorbing region near the base of the supergiant companion's wind. 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 increase in the power law photon index 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.Comment: 22 pages, 27 figures, accepted for publication in MNRAS after
moderate revisio
