Rapid luminosity decline and subsequent reformation of the innermost dust distribution in the changing-look AGN Mrk 590
Rapid luminosity decline and subsequent reformation of the innermost dust distribution in the changing-look AGN Mrk 590
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DOI：
10.1093/mnras/stz3397
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发表时间：
2019-04
影响因子：
4.8
通讯作者：
M. Kokubo;T. Minezaki
中科院分区：
文献类型：
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作者：
M. Kokubo;T. Minezaki
我们研究了1998至2007年间“变脸”的活动星系核(AGN)MRK 590的长期光学/近红外(NIR)通量变异性。来自SDSS STRIPE 82数据库和多色活动星系核监测(MAGNUM)项目的多波段多历元光学/近红外测光数据显示，在2000-2001年间，MRK 590的光度突然下降。由Magnum计划在2003年至2007年的微弱状态下获得的V和K波段光曲线之间的尘埃混响滞后信号的检测表明，由于前述活动星系核光度的显著下降，到2004年，MRK590的尘埃环最内侧半径Rust已经变得非常小[Rust≃32光日(lt天)]。弱态的辐射尘埃与1990年至1996年由以往混响映射观测测得的RHβ、BLR26天的Hβ宽线区半径相当。这些观测表明，在AGN紫外线光度下降后，MRK590中尘环的最内侧半径迅速减小，最内侧尘埃分布的补给时间尺度小于4年，远短于BLR气体或尘埃云的自由落体时间尺度。我们认为，最内部尘埃分布的快速补充可以通过辐射冷却的BLR气云中的新尘埃形成，或者通过由于辐射压力而在圆盘大气中形成新的尘埃和随后来自尘埃盘的垂直风来实现。
We examine the long-term optical/near-infrared (NIR) flux variability of a ‘changing-look’ active galactic nucleus (AGN) Mrk 590 between 1998 and 2007. Multiband multi-epoch optical/NIR photometry data from the SDSS Stripe 82 data base and the Multicolor Active Galactic Nuclei Monitoring (MAGNUM) project reveal that Mrk 590 experienced a sudden luminosity decrease during the period from 2000 to 2001. Detection of dust reverberation lag signals between V- and K-band light curves obtained by the MAGNUM project during the faint state in 2003–2007 suggests that the dust torus innermost radius Rdust of Mrk 590 had become very small [Rdust ≃ 32 light-days (lt-days)] by the year 2004 according to the aforementioned significant decrease in AGN luminosity. The Rdust in the faint state is comparable to the H β broad-line region (BLR) radius of RH β, BLR ≃ 26 lt-days measured by previous reverberation mapping observations during the bright state of Mrk 590 in 1990–1996. These observations indicate that the innermost radius of the dust torus in Mrk 590 decreased rapidly after the AGN ultraviolet-optical luminosity drop, and that the replenishment time-scale of the innermost dust distribution is less than 4 yr, which is much shorter than the free fall time-scale of BLR gas or dust clouds. We suggest that rapid replenishment of the innermost dust distribution can be accomplished either by new dust formation in radiatively cooled BLR gas clouds or by new dust formation in the disc atmosphere and subsequent vertical wind from the dusty disc as a result of radiation pressure.