利用AGN光变曲线映射吸积盘温度涨落
Using AGN lightcurves to map accretion disc temperature fluctuations
摘要：
我们介绍了一个新的模型来理解活动星系核的连续可变性。我们从一个Shakura-Sunyaev薄吸积盘与稳态径向温度剖面$T(R)$和假设的变化的流量是由于轴对称的温度扰动$δT(R,t)$。线性化方程后，我们拟合紫外光学活动星系核的光变曲线，以确定$δT(R,t)$的样品的七个活动星系核。我们看到了多样性的$|δT/T| \sim 0.1$波动模式，这是不占主导地位的传出波以光速传播的“灯柱”模型用于解释光盘混响映射研究的预期。相反，最常见的模式类似于慢（$v \ll c$）传入波。对我们发现的一种解释是，这些进入的波触发了中心温度波动，这些波动就像灯柱一样，产生了以光速向外移动的较低幅度的温度波动。光变曲线由灯柱信号主导--尽管温度波动由具有类似可变性时间尺度的其他结构主导--因为圆盘以指数方式平滑了来自较慢移动（$v \ll c$）波动对观察到的光变曲线的贡献。这导致了光变曲线，非常类似于灯柱模型的预期，但具有缓慢的变化时间尺度的传入波。这也意味着更长时间尺度的变化信号将越来越偏离灯柱模型，因为随着其周期或空间波长的增加，移动较慢的波的平滑度稳步下降。
英文摘要：
We introduce a new model for understanding AGN continuum variability. We start from a Shakura--Sunyaev thin accretion disc with a steady-state radial temperature profile $T(R)$ and assume that the variable flux is due to axisymmetric temperature perturbations $δT(R,t)$. After linearizing the equations, we fit UV-optical AGN lightcurves to determine $δT(R,t)$ for a sample of seven AGNs. We see a diversity of $|δT/T| \sim 0.1$ fluctuation patterns which are not dominated by outgoing waves traveling at the speed of light as expected for the "lamppost" model used to interpret disc reverberation mapping studies. Rather, the most common pattern resembles slow ($v \ll c$) ingoing waves. An explanation for our findings is that these ingoing waves trigger central temperature fluctuations that act as a lamppost, producing lower amplitude temperature fluctuations moving outwards at the speed of light. The lightcurves are dominated by the lamppost signal -- even though the temperature fluctuations are dominated by other structures with similar variability time-scales -- because the discs exponentially smooth the contributions from the slower moving ($v \ll c$) fluctuations to the observed lightcurves. This leads to lightcurves that closely resemble the expectations for a lamppost model but with the slow variability time-scales of the ingoing waves. This also implies that longer time-scale variability signals will increasingly diverge from lamppost models because the smoothing of slower-moving waves steadily decreases as their period or spatial wavelength increases.
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