Variability and the Size–Luminosity Relation of the Intermediate-mass AGN in NGC 4395
Cho, Hojin; Woo, Jong-Hak; Hodges-Kluck, E; Son, Donghoon; Shin, Jaejin; Gallo, Elena; Bae, Hyun-Jin; Brink, T. G; Cho, Wanjin; Filippenko, A. V; Horst, J. C; Ilic, Dragana; Joner, M. D; Kang, Daeun; Kang, Wonseok; Kaspi, Shai; Kim, Taewoo; Kovacevic, A. B; Kumar, S; Le, Huynh Anh N; Nadzhip, A. E; Nunez, F. P; Metlov, V. G; Oknyansky, V. L; Park, Songyoun; Popovic, L. C; Rakshit, S; Schramm, M; Shatsky, N. I; Spencer, M; Sung, E.-H; Sung, H.-i; Tatarnikov, A. M; Vince, O
Date:
2020-04-01
Abstract:
We present a variability study of the lowest-luminosity Seyfert 1 nucleus of the galaxy NGC 4395 based on
photometric monitoring campaigns in 2017 and 2018. Using 22 ground-based and space telescopes, we monitored
NGC 4395 with a ∼5-minute cadence during a period of 10 days and obtained light curves in the ultraviolet (UV),
V, J, H, and K/Ks bands, as well as narrowband Hα. The rms variability is ∼0.13 mag in the Swift UVM2 and V
filter light curves, decreasing down to ∼0.01 mag in the K filter. After correcting for the continuum contribution to
the Hα narrow band, we measured the time lag of the Hα emission line with respect to the V-band continuum as
-
+ 55 31
27– -
+ 122 67
33 minutes in 2017 and -
+ 49 14
15– -
+ 83 14
13 minutes in 2018, depending on assumptions about the continuum
variability amplitude in the Hα narrow band. We obtained no reliable measurements for the continuum-tocontinuum lag between UV and V bands and among near-IR bands, owing to the large flux uncertainty of UV
observations and the limited time baseline. We determined the active galactic nucleus (AGN) monochromatic
luminosity at 5100 Å, l l =´ ( ) - L 5.75 0.40 10 erg s 39 1, after subtracting the contribution of the nuclear star
cluster. While the optical luminosity of NGC 4395 is two orders of magnitude lower than that of other
reverberation-mapped AGNs, NGC 4395 follows the size–luminosity relation, albeit with an offset of 0.48 dex
(>2.5σ) from the previous best-fit relation of Bentz et al
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