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Date and Time of the Query: 2019-06-16 T07:47:07 PDT
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For refcode 2006ApJ...639...46S:
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NED Abstract

Copyright by American Astronomical Society. Reproduced by permission
2006ApJ...639...46S Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies Masahiro Suganuma, Yuzuru Yoshii, Yukiyasu Kobayashi, Takeo Minezaki, Keigo Enya, Hiroyuki Tomita, Tsutomu Aoki, Shintaro Koshida, and Bruce A. Peterson Abstract. The most intense monitoring observations yet made in the optical and near-infrared wave bands were carried out for Seyfert 1 galaxies NGC 5548, NGC 4051, NGC 3227, and NGC 7469 by the MAGNUM telescope, and clear time-delayed responses of the K-band flux variations to the V-band flux variations were found for all of these galaxies. Their H-K color temperatures of 1500 -- 1800 K, estimated from their observed flux variation gradients, support a view that the bulk of the K flux should originate in the thermal radiation of hot dust surrounding the central engine and that the lag time should correspond to light-travel distance between them. Cross-correlation analysis measures their lag times to be 47 -- 53 (NGC 5548), 11 -- 18 (NGC 4051), about 20 (NGC 3227), and 65 -- 87 (NGC 7469) days. The lag times are tightly correlated with the optical luminosities, as expected from dust reverberation ({DELTA}t is proportional to L^0.5^), while weakly with the central virial masses, which suggests that the inner radii of the dust tori around active nuclei have one-to-one correspondences with their central luminosities. In the lag time versus central luminosity diagram, the K-band lag times place an upper boundary on the similar lag times of broad emission lines in the literature, which not only supports the unified scheme of AGNs but also implies a physical transition from the BLR out to the dust torus that encircles the BLR. Correlated short-term V-band and X-ray flux variations in NGC 5548 are also found with a delay of 1 or 2 days, indicating the thermal reprocessing of X-ray emission by the central accretion flow. Key words: ISM: Dust, Extinction, Galaxies: Active, Galaxies: Individual: NGC 3227, Galaxies: Individual: NGC 4051, Galaxies: Individual: NGC 5548, Galaxies: Individual: NGC 7469, Galaxies: Seyfert, Infrared: Galaxies
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