New changing look case in NGC 1566

We present 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 2007-2018. We also report on our optical spectroscopy at the South African Astronomical Observatory with the 1.9-m telescope on the night 2018 August 2-3. A substantial increase in X-ray flux by 1.5 orders of magnitude was observed following the brightening in the UV and optical bands during the last year. After a maximum was reached at the beginning of 2018 July the fluxes in all bands decreased with some fluctuations. The amplitude of the flux variability is strongest in the X-ray band and decreases with increasing wavelength. Low-resolution spectra reveal a dramatic strengthening of the broad emission as well as high-ionization [Fe X] 6374 angstrom lines. These lines were not detected so strongly in the past published spectra. The change in the type of the optical spectrum was accompanied by a significant change in the X-ray spectrum. All these facts confirm NGC 1566 to be a changing look Seyfert galaxy

The post-maximum behaviour of the changing-look Seyfert galaxy NGC 1566

We present results of the long-term multiwavelength 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 2018 August and 2019 September. This paper concentrates on the remarkable post-maximum behaviour after 2018 July when all bands decreased with some fluctuations. We observed three significant re-brightenings in the post-maximum period during 2018 November 17-2019 January 10, 2019 April 29-2019 June 19, and 2019 July 27-2019 August 6. An X-ray flux minimum occurred in 2019 March. The UV minimum occurred about 3 months later. It was accompanied by a decrease of the L-UV/LX-ray ratio. New post-maximum spectra covering (2018 November 31-2019 September 23) show dramatic changes compared to 2018 August 2, with fading of the broad lines and [Fe X] lambda 6374 until 2019 March. These lines became somewhat brighter in 2019 August-September. 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 per cent for minimum in 2014 and 2.8 per cent for maximum in 2018

Variability and the Size-Luminosity Relation of the Intermediate-mass AGN in NGC 4395

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 similar to 5-minute cadence during a period of 10 days and obtained light curves in the ultraviolet (UV), V, J, H, and K/K-s bands, as well as narrowband H alpha. The rms variability is similar to 0.13 mag in the Swift UVM2 and V filter light curves, decreasing down to similar to 0.01 mag in the K filter. After correcting for the continuum contribution to the H alpha narrow band, we measured the time lag of the H alpha emission line with respect to the V-band continuum as minutes in 2018, depending on assumptions about the continuum variability amplitude in the H alpha narrow band. We obtained no reliable measurements for the continuum-to-continuum 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 A, 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 (>= 2.5 sigma) from the previous best-fit relation of Bentz et al