Monitoring the Superorbital Period Variation and Spin Period Evolution of SMC X-1
Monitoring the Superorbital Period Variation and Spin Period Evolution of SMC X-1
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DOI：
10.3847/1538-4357/ab48e4
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发表时间：
2019-10
期刊：
影响因子：
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通讯作者：
Chin-Ping Hu;T. Mihara;M. Sugizaki;Y. Ueda;T. Enoto
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作者：
Chin-Ping Hu;T. Mihara;M. Sugizaki;Y. Ueda;T. Enoto
X射线脉冲星SMC X-1在X射线波段表现出周期长度不稳定的超轨道调制。我们提出了它的定时行为，包括自旋，轨道和超轨道调制，超出了罗西X射线定时探测器使命结束。由小波Z变换和希尔伯特-黄变换得到的时频图表明，在2015年3月的MJD 57，100中发生了一个新的超轨道周期漂移事件。这表明，漂移是经常性的，可能是（准）周期性的。利用全天空X射线图像监测仪（MAXI）获得的硬度比表明，在超轨道周期中从高态到低态的过渡期间，吸收增加。与常规历元相比，漂移历元期间的超轨道轮廓具有较浅且较窄的谷，可能是由较平坦的翘曲引起的。通过使用MAXI气体狭缝相机在2-20 keV范围内跟踪自旋周期演化，我们得出了MJD 55，141（2009年11月）和58，526（2019年2月）之间的平均自旋上升速率为ν stec = 2.515（3）× 10 − 11 s−2。我们得到的自旋频率残差和超轨道频率之间没有正相关，但扭矩的变化伴随着超轨道周期偏移是可能的。我们认为中子星星上的吸积力矩可以通过各种机制来改变，包括质量吸积率和翘曲角的改变。我们将轨道衰变的值更新为P orb / P orb =-3.380（6）× 10 - 6 yr-1。最后，我们再次确认了超轨道调制在光学波段的探测及其与X射线调制的相位相干性。
The X-ray pulsar SMC X-1 shows a superorbital modulation with an unstable cycle length in the X-ray band. We present its timing behaviors, including the spin, orbital, and superorbital modulations, beyond the end of the Rossi X-ray Timing Explorer mission. The time-frequency maps derived by the wavelet Z-transform and the Hilbert–Huang transform suggest that a new superorbital period excursion event occurred in ∼MJD 57,100 (2015 March). This indicates that the excursion is recurrent and probably (quasi)periodic. The hardness ratio obtained with the Monitor of All-sky X-ray Image (MAXI) suggests increased absorption during the transition from the high to the low state in the superorbital cycle. Compared to the regular epochs, the superorbital profile during the excursion epochs has a shallower and narrower valley, likely caused by a flatter warp. By tracking the spin period evolution with the MAXI Gas Slit Camera in 2–20 keV, we derive an averaged spin-up rate of ν ˙ = 2.515 ( 3 ) × 10 − 11 s−2 during the period between MJD 55,141 (2009 November) and 58,526 (2019 February). We obtain no positive correlation between the spin frequency residual and the superorbital frequency, but a torque change accompanying the superorbital period excursion is possible. We suggest that the accretion torque on the neutron star could be changed by various mechanisms, including the change of mass accretion rate and the warp angle. We update the value of the orbital decay as P ˙ orb / P orb = − 3.380 ( 6 ) × 10 − 6 yr−1. Finally, we reconfirm the detection of the superorbital modulation in the optical band and its coherence in phase with the X-ray modulation.