4U 1626-67 X射线脉冲再处理的SALT观察
SALT observation of X-ray pulse reprocessing in 4U 1626-67
摘要：
我们调查的光学再处理的X射线在LMXB脉冲星4U 1626-67在其当前的自旋阶段使用的观测与南部非洲大望远镜（SALT），近同时的观测与Swift-XRT和非同步RXTE-PCA观测，并提出了定时分析的结果。利用2014年3月5日和6日进行的SALT观测，我们发现了一些有趣的后处理特征。在3月5日48 mHz的功率密度谱中，我们检测到一个微弱的光学准周期振荡（QPO），其均方根值为3.3%，尽管在自旋上升阶段没有相应的X射线QPO。在3月5日获得的光变曲线中，我们检测到自旋周期为~7.677 s的相干脉动。在129.92 mHz处还检测到先前已知的略微下移的边带。主脉冲和这个边带之间的频率间隔与早期的观测结果不同，尽管这种差异的统计意义是有限的。3月6日的光变曲线显示了短时间尺度的变化，以耀斑的形式出现在几分钟的时间尺度上。从这一夜的数据得到的折叠脉冲轮廓显示了脉冲峰值漂移的有趣趋势。这种漂移可能是由于i）后处理剂的快速变化，如围绕中子星的吸积盘翘曲的轨道运动，或ii）X射线的内在脉冲相位变化。我们还检查了一些X射线光变曲线与RXTE-PCA在2008-2010年期间获得的脉冲形状的变化，在短时间尺度的X射线耀斑。
英文摘要：
We investigate optical reprocessing of X-rays in the LMXB pulsar 4U 1626-67 in its current spin-up phase using observations with Southern African Large Telescope (SALT), near-simultaneous observations with Swift-XRT and non-simultaneous RXTE-PCA observations and present the results of timing analysis. Using SALT observations carried out on 5th and 6th March, 2014, we detect some interesting reprocessing signatures. We detect a weak optical Quasi Periodic Oscillation (QPO) in the power density spectrum on March 5th at 48 mHz with a fractional rms of 3.3% in spite of the fact that source shows no corresponding X-ray QPO in the spin-up phase. In the light curve obtained on March 5th, we detect a coherent pulsation at the spin period of ~7.677 s. A previously known, slightly down-shifted side-band is also detected at 129.92 mHz. The frequency spacing between main pulse and this side-band is different from earlier observations, though the statistical significance of the difference is limited. The light curve of 6th March displays short time-scale variability in the form of flares on timescales of a few minutes. Folded pulse profiles resulting from data of this night show an interesting trend of pulse peak drifting. This drift could be due to i) rapid changes in the reprocessing agent, like orbital motion of an accretion disk warp around the neutron star or ii) intrinsic pulse phase changes in X-rays. We also examine some X-ray light curves obtained with RXTE-PCA during 2008-2010 for pulse shape changes in short time scales during X-ray flares.
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