Rapid Luminosity Decline and Subsequent Reformation of the Innermost Dust Distribution in the Changing-look AGN Mrk 590. (arXiv:1904.08946v1 [astro-ph.GA])

Rapid Luminosity Decline and Subsequent Reformation of the Innermost Dust Distribution in the Changing-look AGN Mrk 590. (arXiv:1904.08946v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kokubo_M/0/1/0/all/0/1">Mitsuru Kokubo</a> (Tohoku University), <a href="http://arxiv.org/find/astro-ph/1/au:+Minezaki_T/0/1/0/all/0/1">Takeo Minezaki</a> (The University of Tokyo)

We examined long-term optical/near-infrared (NIR) flux variability of a
“changing-look” active galactic nucleus (AGN) Mrk 590 between 1998 and 2007.
Multi-band multi-epoch optical/NIR photometry data from the SDSS Stripe 82
database 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 $R_{dust}$ of Mrk 590
had become very small ($R_{dust} simeq 32$ light-days) by the year 2004
according to the aforementioned significant decrease in AGN luminosity. The
$R_{dust}$ in the faint state is comparable to the H$beta$ broad line region
(BLR) radius of $R_{Hbeta, BLR} simeq 26$ light-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 years, 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 (1) new dust formation in
radiatively-cooled BLR gas clouds or (2) new dust formation in the disk
atmosphere and subsequent vertical wind from the dusty disk launched by
radiation pressure.

We examined long-term optical/near-infrared (NIR) flux variability of a
“changing-look” active galactic nucleus (AGN) Mrk 590 between 1998 and 2007.
Multi-band multi-epoch optical/NIR photometry data from the SDSS Stripe 82
database 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 $R_{dust}$ of Mrk 590
had become very small ($R_{dust} simeq 32$ light-days) by the year 2004
according to the aforementioned significant decrease in AGN luminosity. The
$R_{dust}$ in the faint state is comparable to the H$beta$ broad line region
(BLR) radius of $R_{Hbeta, BLR} simeq 26$ light-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 years, 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 (1) new dust formation in
radiatively-cooled BLR gas clouds or (2) new dust formation in the disk
atmosphere and subsequent vertical wind from the dusty disk launched by
radiation pressure.

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