Long term flux variations in Cen X-3: clues from flux dependent orbital modulation and pulsed fraction

TL;DR

This study analyzes long-term flux variations in Cen X-3, revealing flux-dependent orbital modulation and pulsed fraction changes, suggesting obscuration effects and scattering processes, with possible influence from a precessing accretion disk.

Contribution

It provides new insights into the flux-dependent orbital modulation and pulsed fraction behavior of Cen X-3, highlighting the role of obscuration and scattering in different flux states.

Findings

High state shows sharp eclipse ingress and egress.

Low state exhibits smooth flux variation with orbital phase.

Flux variations are primarily due to obscuration and scattering effects.

Abstract

We have investigated the long term flux variation in Cen X-3 using orbital modulation and pulsed fraction in different flux states using observations made with the All Sky Monitor and the Proportional Counter Array on board the Rossi X-ray Timing Explorer. In the high state, the eclipse ingress and egress are found to be sharp whereas in the intermediate state the transitions are more gradual. In the low state, instead of eclipse ingress and egress, the lightcurve shows a smooth flux variation with orbital phase. The orbital modulation of the X-ray lightcurve in the low state shows that the X-ray emission observed in this state is from an extended object. The flux dependent orbital modulations indicate that the different flux states of Cen X-3 are primarily due to varying degree of obscuration. Measurement of the pulsed fraction in different flux states is consistent with the X-ray emission of Cen X-3 having one highly varying component with a constant pulsed fraction and an unpulsed component and in the low state, the unpulsed component becomes dominant. The observed X-ray emission in the low state is likely to be due to scattering of X-rays from the stellar wind of the companion star. Though we can not ascertain the origin and nature of the obscuring material that causes the aperiodic long term flux variation, we point out that a precessing accretion disk driven by radiative forces is a distinct possibility.