变化形态的活动星系核中X射线日冕的破坏和再生
The destruction and recreation of the X-ray corona in a changing-look Active Galactic Nucleus
摘要：
我们介绍了活动星系核1 ES 1927+654的X射线性质的急剧变化，在一个改变外观的事件。在光学/紫外爆发之后，在X射线日冕中产生的幂律分量消失了，1 ES 1927+65的光谱反而变成由黑体分量（$kT\sim 80-120$ eV）主导。这意味着活动星系核中普遍存在的X射线日冕在这次事件中被破坏了。我们的高密度$\sim 450$全天X射线监测显示，该源在X射线波段变化极大。在长时间尺度上，源在$\sim 100$天内变化到$\sim 4$ dex，而在短时间尺度上，在$\sim 8$小时内变化到$\sim2$ dex。发现源的光度首先表现出强烈的下降到$\sim 10^{40}\rm\,erg\,s^{-1}$，然后在光度不断增加的水平超过爆发前的水平$\gtrsim $ 300天后的光学事件检测，上升到渐进的$\sim 2\times10^{44}\rm\,erg\,s^{-1}$。随着源的X射线光度增加，X射线日冕被重新产生，并且非常陡峭的幂律分量（$Γ\simeq 3$）再次出现，并且在事件开始后的几天内主导0.3-2 keV光度$\gtrsim 10^{43.7}\rm\,erg\,s^{-1}$、$\sim 300$的发射。我们讨论了这一事件的可能起源，并推测我们的观察可以解释的吸积流和碎片之间的相互作用，从潮汐中断的恒星。我们的研究结果表明，改变外观的事件可以与吸积SMBHs的最里面的区域的戏剧性和快速的转变。
英文摘要：
We present the drastic transformation of the X-ray properties of the active galactic nucleus 1ES 1927+654, following a changing-look event. After the optical/UV outburst the power-law component, produced in the X-ray corona, disappeared, and the spectrum of 1ES 1927+65 instead became dominated by a blackbody component ($kT\sim 80-120$ eV). This implies that the X-ray corona, ubiquitously found in AGN, was destroyed in the event. Our dense $\sim 450$ day long X-ray monitoring shows that the source is extremely variable in the X-ray band. On long time scales the source varies up to $\sim 4$ dex in $\sim 100$ days, while on short timescales up to $\sim2$ dex in $\sim 8$ hours. The luminosity of the source is found to first show a strong dip down to $\sim 10^{40}\rm\,erg\,s^{-1}$, and then a constant increase in luminosity to levels exceeding the pre-outburst level $\gtrsim $300 days after the optical event detection, rising up asymptotically to $\sim 2\times10^{44}\rm\,erg\,s^{-1}$. As the X-ray luminosity of the source increases, the X-ray corona is recreated, and a very steep power-law component ($Γ\simeq 3$) reappears, and dominates the emission for 0.3-2 keV luminosities $\gtrsim 10^{43.7}\rm\,erg\,s^{-1}$, $\sim 300$ days after the beginning of the event. We discuss possible origins of this event, and speculate that our observations could be explained by the interaction between the accretion flow and debris from a tidally disrupted star. Our results show that changing-look events can be associated with dramatic and rapid transformations of the innermost regions of accreting SMBHs.
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