Signal from neutron star obscured by oscillating accretion torus

Proceedings of RAGtime / Signal from neutron star obscured by oscillating accretion torus

Signal from neutron star obscured by oscillating accretion torus

Authors

Kateřina Klimovičová, Debora Lančová and Gabriel Török

Abstract

X-ray fluxes of low-mass neutron star binaries reveal rapid, nearly periodic changes corresponding to frequencies in the order of hundreds of hertz. Two closely related peaks often appear in the power spectral density and are designated as twin-peak Quasi-Periodic Oscillations (QPOs). Some QPO models attribute the observed effects to the torus oscillating in the inner region of the accretion flow. Since the observed variability is very strong, oscillations of a torus can be reflected in the observed light curves either by modulation of an accretion flow and/or by a periodic obscuration of a hot region on the neutron star surface. Applying a self-consistent description of the oscillations and full relativistic ray tracing, we analyse how the obscuration effect can affect the light curve detected by a distant observer. Within the same paradigm, we also investigate a possible product of torus instability and the implied signature of the Keplerian frequency in the light curve.

Keywords

Black hole – neutron star – X–ray binary – rapid variability

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