ULTI-WAVELENGTH MONITORING OF THE CHANGING-LOOK AGN NGC 2617 DURING STATE CHANGES

V. L. Oknyansky, C. M. Gaskell, N. A. Huseynov, Kh. M. Mikailov, V. M. Lipunov, N. I. Shatsky, S. S. Tsygankov, E. S. Gorbovskov, A. M. Tatarnikov, V. G. Metlov, K. L. Malanchev, M. B. Brotherton, D. Kasper, P. Du, X. Chen, M. A. Burlak, D. A. H. Buckley, R. Rebolo, M. Serra-Ricart, R. Podesta, H. Levato

Анотація


Optical  and  near-infrared  photometry, optical spectroscopy, and  soft X-ray and UV  monitoring of  the  changing-look  active  galactic  nucleus  NGC  2617 show that it continues to have the appearance of a type-1 Seyfert galaxy. An optical light curve for 2010–2017 indicates that the change of type probably occurred between  2010 October and 2012 February and  was not related to the  brightening  in  2013.  In  2016  and  2017  NGC  2617 brightened again to a level of activity close to that in 2013 April. However, in 2017 from the end of the March to end of  July  2017  it  was  in  very  low  level  and  starting  to change  back  to  a  Seyfert  1.8.  We  find  variations  in  all passbands  and  in  both  the  intensities  and  profiles  of  the broad  Balmer  lines.  A  new  displaced  emission  peak  has appeared in Hβ. X-ray variations are well correlated with UV–optical variability and possibly lead by ~2–3 d. The K band lags the J band by about 21.5 ± 2.5 d and lags the combined B + J bands by ~25 d. J lags B by about 3 d. This  could  be  because  J-band  variability  arises  predominantly from the outer part of the accretion disc, while K-band  variability  is  dominated  by  thermal  re-emission  by dust. We propose that spectral-type changes are a result of increasing  central  luminosity  causing  sublimation  of  the innermost  dust  in  the  hollow  bi-conical  outflow.  We briefly  discuss  various  other  possible  reasons  that  might explain the dramatic changes in NGC 2617.


Ключові слова


AGN; CL AGN; X-ray; UV; optical; photometry; spectroscopy

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DOI: https://doi.org/10.18524/1810-4215.2017.30.114366

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