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

Abstract

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.

11 pages, 9 figured, accepted for publication in MNRAS

References in corpus (14)

• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Mid-infrared variability of changing-look AGN
• New changing look case in NGC 1566
• Long-term variability of the optical spectra of NGC 4151: I. Light curves and flux correlations
• Ultraviolet and X-ray variability of active galactic nuclei with Swift
• Long-term optical spectral monitoring of a changing-look AGN NGC 3516 I: Continuum and broad-line flux variability
• Coronal-Line Forest AGN: the best view of the inner edge of the AGN torus?
• WALLABY Early Science - III. An HI Study of the Spiral Galaxy NGC 1566
• NGC 1566: analysis of the nuclear region from optical and near-infrared Integral Field Unit spectroscopy
• Variability of the coronal line region in NGC 4151
• The Large Amplitude X-ray Variability in NGC 7589: Possible Evidence for Accretion Mode Transition
• The Relative Wavelength Independence of IR Time Lags in NGC4151 During the Years 2010-2015

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