The long-term optical and near infrared monitoring observations for a type 1 act ive galactic nucleus NGC 4151 were carried out for six years from 2001 to 2006 b y using the MAGNUM telescope, and delayed response of flux variations in the $K(2.2μm)$ band to those in the $V(0.55μm)$ band was clearly detected. Based on cross correlation analysis, we precisely measured a lag time $Δt$ for eight separate periods, and we found that $Δt$ is not constant changing be tween 30 and 70 days during the monitoring period. Since $Δt$ is the ligh t travel time from the central energy source out to the surrounding dust torus, this is the first convincing evidence that the inner radius of dust torus did ch ange in an individual AGN. In order to relate such a change of $Δt$ with a change of AGN luminosity $L$, we presented a method of taking an average of th e observed $V$-band fluxes that corresponds to the measured value of $Δt$, and we found that the time-changing track of NGC 4151 in the $Δt$ versus $L$ diagram during the monitoring period deviates from the relation of $Δt \propto L^{0.5}$ expected from dust reverberation. This result, combined with t he elapsed time from period to period for which $Δt$ was measured, indicat es that the timescale of dust formation is about one year, which should be taken into account as a new constraint in future studies of dust evolution in AGNs.
Coronal-Line Forest AGN: the best view of the inner edge of the AGN torus?
我们介绍冕线森林活动星系核（CLiF AGN），AGN具有丰富的禁止高电离线（FHILs，例如[FeVII]，[FeX]和[NeV]），以及相对较强的窄（$\sim$ 300 km s $^{-1}$）H $α$发射相比，其他巴耳末过渡线。我们发现，CLiF发射区的运动学是类似的禁戒低电离发射线（FLIL）区域。我们将FHIL和FLIL的发射线强度与CLOUDY光电离结果进行比较，发现当与FLIL发射区（10 $^{3.0}$ $<$ n $_H$ $<$ 10 $^{7.5}$ cm $^{-3}$）相比时，CLiF发射区具有更高的密度（10 $^{4.5}$ $<$ n $_H$ $<$ 10 cm $^{-3}$）。我们使用光电离的结果来计算CLiF区域的径向距离（0.04 $<$ R $_{CLiF}$ $<$ 32.5 pc），并发现它们是可比的尘埃颗粒升华距离（0.10 $<$ R $_{SUB}$ $<$ 4.3 pc）。因此，我们认为，内环面壁是最有可能的位置的CLiF区域，和不寻常的强度的FHILs是由于一个特定的视角给出了一个最大的视图的远壁的环面没有连续被发现。
