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arXiv 1605.00546astro-ph.HE
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Sco X-1的Kepler K2观测:轨道调制和与费米GBM和MAXI的关联

Kepler K2 Observations of Sco X-1: Orbital Modulations and Correlations with Fermi GBM and MAXI

R. I. Hynes, B. E. Schaefer, Z. A. Baum, C. -C. Hsu, M. L. Cherry, S. Scaringi

摘要:

利用Kepler K2光学数据和Fermi GBM和MAXI X射线数据对低质量X射线双星Sco X-1进行了多波长研究。我们从开普勒数据中恢复了一个清晰的正弦轨道调制。光通量在平均轨道光变曲线周围呈双峰分布,高态和低态都显示出相同的调制。高态与Z图的外展分支大致一致,低态与正常分支大致一致。我们在高状态下看到快速的光学耀斑和缓慢的下降,在低状态下看到缓慢的增亮。高状态耀斑表现出一个狭窄的振幅范围,在最大振幅处有一个引人注目的截止。光通量在高态下与X射线通量相关,但在低态下它们是反相关的。这些模式可以在通量-通量图和交叉关联函数中清楚地看到,并且在MAXI和GBM之间是一致的。高状态相关性迅速出现,最多有几分钟的滞后。我们把这归因于X射线耀斑的热再处理。低态反相关更宽,与零和3分钟之间的光学滞后一致,并且相对于高能X射线最强。我们认为,在低状态下的光通量的减少可能反映了光盘照射的效率降低,所造成的照明几何形状的变化。这些变化可以反映遮蔽的垂直范围或覆盖因子或散射材料的光学深度。

英文摘要:

We present a multi-wavelength study of the low-mass X-ray binary Sco X-1 using Kepler K2 optical data and Fermi GBM and MAXI X-ray data. We recover a clear sinusoidal orbital modulation from the Kepler data. Optical fluxes are distributed bimodally around the mean orbital light curve, with both high and low states showing the same modulation. The high state is broadly consistent with the flaring branch of the Z diagram and the low state with the normal branch. We see both rapid optical flares and slower dips in the high state, and slow brightenings in the low state. High state flares exhibit a narrow range of amplitudes with a striking cut-off at a maximum amplitude. Optical fluxes correlate with X-ray fluxes in the high state, but in the low state they are anti-correlated. These patterns can be seen clearly in both flux-flux diagrams and cross-correlation functions and are consistent between MAXI and GBM. The high state correlation arises promptly with at most a few minutes lag. We attribute this to thermal reprocessing of X-ray flares. The low state anti-correlation is broader, consistent with optical lags of between zero and 3 ~min, and strongest with respect to high energy X-rays. We suggest that the decreases in optical flux in the low state may reflect decreasing efficiency of disc irradiation, caused by changes in the illumination geometry. These changes could reflect the vertical extent or covering factor of obscuration or the optical depth of scattering material.

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