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arXiv 0902.4632astro-ph.HE
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GX 9+9:X射线轨道调制的可变性

GX 9+9: Variability of the X-Ray Orbital Modulation

Robert J. Harris, Alan M. Levine, Martin Durant, Albert K. H. Kong, Phil Charles, Tariq Shahbaz

摘要:

本文介绍了Rossi X射线定时探测器上的全天监视器(ASM)和正比计数器阵列(PCA)对银河系核球X射线源GX 9+9的观测结果。ASM的结果表明,赫兹和伍德在1987年首次报告的4.19小时X射线周期性在2004年底之前的大部分任务中很弱或没有检测到,但随后变得很强,并保持了大约2年,之后大大减弱。当在4.19小时周期的调制是强的,它出现在折叠光变曲线的强度下降略小于30%的周期,是明显的非正弦曲线。在强调制出现之前,对GX 9+9进行了一些PCA观测;其中两次是在2006年强调制时期进行的。从早期的PCA观测获得的数据产量在最好的有限的证据存在的相位依赖的强度变化,而从后来的观测数据证实存在的通量最小值的深度和相位兼容的折叠ASM光变曲线。在强调制开始之前的2000年,钱德拉对GX 9+9进行了观测,得到的光变曲线表明,在预测的时间内可能存在浅倾角。在2006年进行的光学观测中,当X射线调制很强时,在4.19小时的周期内没有显示调制程度的增加。被认为是在X射线和其他观测结果的调制强度的变化的影响。

英文摘要:

Results of observations of the Galactic bulge X-ray source GX 9+9 by the All-Sky Monitor (ASM) and Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer are presented. The ASM results show that the 4.19 hour X-ray periodicity first reported by Hertz and Wood in 1987 was weak or not detected for most of the mission prior to late 2004, but then became strong and remained strong for approximately 2 years after which it weakened considerably. When the modulation at the 4.19 hour period is strong, it appears in folded light curves as an intensity dip over slightly less than 30% of a cycle and is distinctly nonsinusoidal. A number of PCA observations of GX 9+9 were performed before the appearance of strong modulation; two were performed in 2006 during the epoch of strong modulation. Data obtained from the earlier PCA observations yield at best limited evidence of the presence of phase-dependent intensity changes, while the data from the later observations confirm the presence of flux minima with depths and phases compatible with those apparent in folded ASM light curves. Light curves from a Chandra observation of GX 9+9 performed in the year 2000 prior to the start of strong modulation show the possible presence of shallow dips at the predicted times. Optical observations performed in 2006 while the X-ray modulation was strong do not show an increase in the degree of modulation at the 4.19 hour period. Implications of the changes in modulation strength in X-rays and other observational results are considered.

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