UNDERSTANDING QUASARS ACROSS COSMIC TIME: THE STRUCTURE OF THE ACCRETION FLOW AROUND A SUPERMASSIVE BLACK HOLE

黑洞是可能存在的最简单的物体，其特征只有质量和自旋。我们最容易通过吸积看到它们，在吸积中，落入的物质释放出巨大的引力势能，将宇宙中最暗的物体变成最亮的。因此，还有另一个参数控制着吸积黑洞的可观测外观，即质量吸积率，以及任何非球形流的视角。基本上，这些参数必须决定大多数属性。标准盘模型似乎主要适用于高亮度的恒星质量黑洞，从双星伴星中吸积物质。但是，在为活动星系核（AGN）提供能量的超大质量黑洞中，可以看到一些非常不同的结构，它们的亮度相似。在质量为108 M的发光AGN中，标准吸积盘的峰值温度<105K，形成非常蓝的光学/紫外连续体。这样的连续性是可以看到的，尽管它们通常不像预期的那样蓝色。紫外线发射的下降似乎与1千电子伏特以下x射线发射的上升有关。光学/紫外线也是可变的，通常在几周的时间尺度上显示出超过10%的变化，然而一个标准的圆盘只能在100 - 104年的时间尺度上对质量吸积率的变化做出反应（例如Noda & Done 2018）。热x射线日冕在更快的时间尺度（天）上是可变的，但它的性质仍然没有被很好地理解。这些数据可以通过吸积流结构变化的模型来拟合，而不是标准的圆盘。这种复合几何形状根据质量、质量吸积率和自旋预测AGN的发射光谱，并预测紫外线和x射线的相对几何形状（Kubota & Done 2018）。这些模型是可测试的，因为它们完全指定了几何形状。可变x射线可以照亮软x射线多余部分和外盘，通过再处理产生可变UV成分，这是照明x射线通量的滞后和平滑版本（Mahmoud & Done 2020）。该项目将计算这种响应，并将其用于密集的监测数据，以探索AGN吸积盘的内部结构，其中大部分的巨大亮度是发射出来的。这将为我们提供一个物理模型来理解宇宙时间内的AGN。

Black holes are the simplest possible objects, characterised only by mass and spin. We see them most easily via accretion, where the enormous gravitational potential energy released by the infalling material transforms these darkest objects in the Universe into the brightest. Hence there is another parameter which controls the observable appearance of an accreting black hole, namely the mass accretion rate, along with viewing angle for any non-spherical flow. Fundamentally, these parameters must determine the majority of the properties. Standard disc models seem to mostly work in stellar mass black holes at high luminosities, accreting material from a binary companion star. But some very different structures are seen for similarly high luminosities in the supermassive black holes powering the Active Galactic Nuclei (AGN). A standard accretion disc in a luminous AGN with mass 108 M has peak temperature of <105K, making a very blue optical/UV continuum. Such continuua are seen, though they are often not as blue as expected. There is a downturn in the UV emission which appears to connect to an upturn in the X-ray emission below 1 keV. The optical/UV is also variable, typically showing changes of more than 10% on timescales of weeks, yet a standard disc can only respond to changes in mass accretion rate on a timescale of > 104 years (e.g. Noda & Done 2018). The hot X-ray corona is variable on even faster timescales (days), but again its nature is not well understood. Instead of a standard disc, the data can be fit by models where the accretion flow structure changes. This composite geometry predicts the emission spectrum of the AGN based on mass, mass accretion rate and spin, and predicts the relative geometry of the UV and X-rays (Kubota & Done 2018). These models are testable, as they completely specify the geometry. The variable X-rays can illuminate the soft X-ray excess and outer disc, producing a variable UV component from reprocessing which is a lagged and smoothed version of the illuminating X-ray flux (Mahmoud & Done 2020). The project will calculate this response, and use this on intensive monitoring data to explore the inner structure of AGN accretion discs, where the majority of their vast luminosity is emitted. This will give us a physical model to understand AGN across cosmic time.