V. L. Oknyansky, H. Winkler, S. S. Tsygankov, V. M. Lipunov, E. S. Gorbovskoy, F. van Wyk, D.A. H. Buckley, N. V. Tyurina


We summarize a study of optical,
UV and X-ray light curves of the nearby changing
look active galactic nucleus in the galaxy NGC 1566
obtained with the Neil Gehrels Swift Observatory and
the MASTER Global Robotic Network over the period
2007-2019. We also report on optical spectroscopy
using the South African Astronomical Observatory
1.9-m telescope between Aug. 2018 and Mar. 2019. A
substantial increase in X-ray flux by 1.5 orders of mag-
nitude was observed following the brightening in the
UV and optical bands during the first half of 2018 year.
After a maximum was reached at the beginning of
July 2018, the fluxes in all bands decreased with some
fluctuations. The most remarkable re-brightenings in
of the light curve following the decline from the bright
phase were observed at MJD range 58440-58494 and
58603-58654. The amplitude of the flux variability
is strongest in the X-ray band and decreases with
increasing wavelength. Low-resolution spectra (Aug
2018) reveal a dramatic strengthening of the broad
emission as well as high-ionization [FeX]6374 lines.
These lines were not detected so strongly in the past
published spectra. The change in the type of the opti-
cal spectrum was accompanied by a significant change
in the X-ray spectrum. For the last optical spectra (31
Nov. 2018 – 28 Mar. 2019) we see dramatic changes
compared to 2 Aug 2018, accompanied by the fading
of broad emission lines and high-ionization [FeX]6374
line. Effectively, two changing look (CL) cases were
observed for this object: changing to Sy1.2 type and
then returning to the low state as Sy 1.8–Sy1.9 type.
Some possible explanations of the observed dramatic
changes are discussed.

Ключові слова

Galsxies; active galaxies; individual: NGC 1566

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