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  • Oknyansky, V L; Brotherton, M S; Tsygankov, S S; Dodin, A V; Tatarnikov, A M; P Du; D -W Bao; Burlak, M A; Ikonnikova, N P; Lipunov, V M; Gorbovskoy, E S; Metlov, V G; Belinski, A A; Shatsky, N I; Zheltouhov, S G; Maslennikova, N A; J -M Wang; Zhai, S; F -N Fang; Fu, Y -X; H -R Bai; Kasper, D; Huseynov, N A; McLane, J N; Maithil, J; Zastrocky, T E; Olson, K A; Chen, X; Chelouche, D; Oknyansky, R S; Buckley, D A H; Tyurina, N V; Kuznetsov, A S; Rebolo, R L; Zhao, B -X

    arXiv (Cornell University), 08/2023
    Paper, Journal Article

    We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC~2617 carried out from 2016 until 2022 and covering the wavelength range from the X-ray to the near-IR. The facilities included the telescopes of the SAI MSU, MASTER Global Robotic Net, the 2.3-m WIRO telescope, Swift, and others. We found significant variability at all wavelengths and, specifically, in the intensities and profiles of the broad Balmer lines. We measured time delays of ~ 6 days (~ 8 days) in the responses of the H-beta (H-alpha) line to continuum variations. We found the X-ray variations to correlate well with the UV and optical (with a small time delay of a few days for longer wavelengths). The K-band lagged the B band by 14 +- 4 days during the last 3 seasons, which is significantly shorter than the delays reported previously by the 2016 and 2017--2019 campaigns. Near-IR variability arises from two different emission regions: the outer part of the accretion disc and a more distant dust component. The HK-band variability is governed primarily by dust. The Balmer decrement of the broad-line components is inversely correlated with the UV flux. The change of the object's type, from Sy1 to Sy1.8, was recorded over a period of ~ 8 years. We interpret these changes as a combination of two factors: changes in the accretion rate and dust recovery along the line of sight.