Cen X-3的长期通量变化：来自通量依赖轨道调制和脉冲分数的线索
Long term flux variations in Cen X-3: clues from flux dependent orbital modulation and pulsed fraction
摘要：
利用Rossi X射线定时探测器上的全天监视器和正比计数器阵列的观测资料，研究了在不同通量状态下，利用轨道调制和脉冲分率观测的Cen X-3的长期通量变化。在高状态下，日食的入口和出口被发现是尖锐的，而在中间状态的过渡是渐进的。在低态，而不是日食的入口和出口，光变曲线显示了一个平滑的通量变化与轨道相位。在低态下X射线光变曲线的轨道调制表明，在这种状态下观察到的X射线发射来自一个扩展的物体。通量相关的轨道调制表明，不同的通量状态的Cen X-3主要是由于不同程度的遮蔽。在不同的通量状态下的脉冲分数的测量是一致的与Cen X-3的X射线发射具有一个高度变化的组件与恒定的脉冲分数和非脉冲的组件和在低状态下，非脉冲的组件成为主导。观测到的低态X射线辐射可能是由于伴星的恒星风散射X射线。虽然我们不能确定造成非周期性长期流量变化的遮蔽物质的来源和性质，但我们指出，由辐射力驱动的进动吸积盘是一种明显的可能性。
英文摘要：
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.
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