Oscillations In Low-mass X-ray Binaries Research Articles

Quasi-Periodic Oscillations in Low-Mass X-ray Binaries

The properties of the rapid, persistent quasi-periodic oscillations (QPO) discovered with EXOSAT in the X-ray flux of at least 7 bright low-mass X-ray binaries are described. Particular attention is given to the various relations observed between QPO frequency and X-ray intensity, the link between QPO and the low-frequency noise in the X-ray intensity and the bimodal properties of in particular Sco X-1, GX 5-1 and Cyg X-2. The merits of the hypothesis that the QPO indicate the presence of a neutron star with a magnetosphere are considered.

A model for quasi-periodic oscillations in low-mass X-ray binaries

Quasi-periodic millisecond oscillations in the X-ray flux of two low-mass X-ray binaries, GX5–1 and ScoX-1, were recently reported1–4. These quasi-periodic fluctuations are very similar to those observed in the soft X-ray flux of some dwarf novae in outburst5,6. Guided by this analogy, we propose here that, as in the case of dwarf novae7, oscillations in low-mass X-ray binaries are caused by transient magnetic fields generated by turbulent dynamo action in the boundary layer and possibly in the corona of the accreting neutron star. The magnetic fields created in this way are too weak to channel the accreting material, but are strong enough to influence the heat transport in the neutron star corona and boundary layer and to cause bright spots with lifetimes of a few rotation periods to appear randomly on the neutron star surface. The rotation of this star's outer layers, together with the appearance and disappearance of the spots at random azimuthal positions, then gives rise to oscillations with the coherence characteristics reported in the observations.