The post-maximum behaviour of the changing-look Seyfert galaxy NGC 1566
  We present results of the long-term multi-wavelength study of optical, UV and
X-ray variability of the nearby changing-look (CL) Seyfert NGC 1566 observed
with the Swift Observatory and the MASTER Global Robotic Network from 2007 to
2019. We started spectral observations with South African Astronomical
Observatory 1.9-m telescope soon after the brightening was discovered in July
2018 and present here the data for the interval between Aug. 2018 to Sep. 2019.
This paper concentrates on the remarkable post-maximum behaviour after July
2018 when all bands decreased with some fluctuations. We observed three
significant re-brightenings in the post-maximum period during 17 Nov. 2018 - 10
Jan. 2019, 29 Apr. - 19 Jun. 2019 and 27 Jul.- 6 Aug. 2019. An X-ray flux
minimum occurred in Mar. 2019. The UV minimum occurred about 3 months later. It
was accompanied by a decrease of the Luv/Lx ratio. New post-maximum spectra
covering (31 Nov. 2018 - 23 Sep. 2019) show dramatic changes compared to 2 Aug.
2018, with fading of the broad lines and [Fe X]6374 until Mar. 2019. These
lines became somewhat brighter in Aug.-Sep. 2019. Effectively, two CL states
were observed for this object: changing to type 1.2 and then returning to the
low state as a type 1.8 Sy. We suggest that the changes are due mostly to
fluctuations in the energy generation. The estimated Eddington ratios are about
0.055% for minimum in 2014 and 2.8% for maximum in 2018.
