SMC X-1漂移的监测观察（MOOSE）- II：一种新的漂移伴随着自旋加速
Monitoring observations of SMC X-1's excursions (MOOSE)-II: A new excursion accompanies spin-up acceleration
摘要：
SMC X-1是一颗高质量X射线双星，具有超轨道调制和不稳定周期。此前的监测显示，1996- 1998年、2005- 2007年和2014- 2016年发生了三次偏离事件。超轨道周期从>60天漂移到<40天，然后在一次漂移中又变回来。本文报道了SMC X-1在2020- 2021年发生的一次新的漂移事件，表明超轨道调制具有不可预测的混沌性质。我们跟踪自旋周期的演变，发现自旋加速率加速一年前开始的新的偏移，这表明一个可能的由内而外的过程连接自旋加速和超轨道偏移。这导致自旋周期残差的偏差，类似于1996- 1998年第一次漂移的行为。在进一步分析脉冲轮廓的演变过程中，我们发现脉冲分数显示出长期的演变，并可能连接到超轨道的漂移。这些发现加深了SMC X-1的神秘性，因为它们不能单独用翘曲圆盘模型来解释。即将到来的有针对性的观测和理论研究可能会提高我们对发生的详细吸积机制的理解。
英文摘要：
SMC X-1 is a high-mass X-ray binary showing superorbital modulation with an unstable period. Previous monitoring shows three excursion events in 1996--1998, 2005--2007, and 2014--2016. The superorbital period drifts from >60 days to <40 days and then evolves back during an excursion. Here we report a new excursion event of SMC X-1 in 2020--2021, indicating that the superorbital modulation has an unpredictable, chaotic nature. We trace the spin-period evolution and find that the spin-up rate accelerated one year before the onset of this new excursion, which suggests a possible inside-out process connecting the spin-up acceleration and the superorbital excursion. This results in a deviation of the spin period residual, similar to the behaviour of the first excursion in 1996--1998. In further analysis of the pulse profile evolution, we find that the pulsed fraction shows a long-term evolution and may be connected to the superorbital excursion. These discoveries deepen the mystery of SMC X-1 because they cannot be solely interpreted by the warped disc model. Upcoming pointed observations and theoretical studies may improve our understanding of the detailed accretion mechanisms taking place.
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