Observational Requirements for High‐Fidelity Reverberation Mapping

We present a series of simulations to demonstrate that high‐fidelity velocity‐delay maps of the emission‐line regions in active galactic nuclei (AGNs) can be obtained from time‐resolved spectrophotometric data sets like those that will arise from the proposed Kronos satellite. While previous reverberation‐mapping experiments have established the size scale R of the broad emission‐line regions from the mean time delay τ = R/c between the line and continuum variations and have provided strong evidence for supermassive black holes, the detailed structure and kinematics of the broad‐line region remain ambiguous and poorly constrained. Here we outline the technical improvements that will be required to successfully map broad‐line regions by reverberation techniques. For typical AGN continuum light curves, characterized by power‐law power spectra P(f)∝f-α with α = -1.5 ± 0.5, our simulations show that a small UV/optical spectrometer like Kronos will clearly distinguish between currently viable alternative kinematic models. From spectra sampled at time intervals Δt and sustained for a total duration Tdur, we can reconstruct high‐fidelity velocity‐delay maps with velocity resolution comparable to that of the spectra, and delay resolution Δτ ≈ 2Δt, provided that Tdur exceeds the broad‐line region light crossing time by at least a factor of 3. Even very complicated kinematical models, such as a Keplerian flow with superimposed spiral wave pattern, are resolved in maps from our simulated Kronos data sets. Reverberation mapping with Kronos data is therefore likely to deliver the first clear maps of the geometry and kinematics in the broad emission‐line regions 1–100 μas from supermassive black holes.

我们进行了一系列模拟，以证明可以从像拟议的克洛诺斯卫星所产生的那种时间分辨分光光度数据集获得活动星系核（AGN）中发射线区域的高保真速度 - 延迟图。虽然先前的 reverberation - mapping（回波映射）实验已经根据谱线和连续谱变化之间的平均时间延迟τ = R/c确定了宽发射线区域的大小尺度R，并为超大质量黑洞提供了有力证据，但宽线区的详细结构和运动学仍然不明确且约束不佳。在此我们概述了通过回波技术成功绘制宽线区所需的技术改进。对于以幂律功率谱P(f)∝f -α（其中α = -1.5 ± 0.5）为特征的典型AGN连续谱光变曲线，我们的模拟表明，像克洛诺斯这样的小型紫外/光学光谱仪将能够清楚地区分当前可行的不同运动学模型。从以时间间隔Δt采样并持续总时长为Tdur的光谱中，我们可以重建高保真速度 - 延迟图，其速度分辨率可与光谱相当，延迟分辨率Δτ ≈ 2Δt，前提是Tdur至少比宽线区的光传播时间长3倍。即使是非常复杂的运动学模型，例如叠加有螺旋波模式的开普勒流，在我们模拟的克洛诺斯数据集的图中也能被分辨出来。因此，利用克洛诺斯数据进行的回波映射很可能会提供距离超大质量黑洞1 - 100微角秒的宽发射线区域的几何形状和运动学的首批清晰图像。