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.

arXiv comment11 pages, 9 figured, accepted for publication in MNRAS

References in corpus (38)

• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• Revisiting the Unified Model of Active Galactic Nuclei
• AGN Black Hole Masses and Bolometric Luminosities
• Master Robotic Net
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• ALMA observations of molecular tori around massive black holes
• Changing-Look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Swift monitoring of NGC 4151: Evidence for a Second X-ray/UV Reprocessing
• Mid-infrared variability of changing-look AGN
• Optical--to--X-ray emission in low-absorption AGN: Results from the Swift-BAT 9 month catalogue
• Long term optical and X-ray variability of the Seyfert galaxy Markarian 79
• New changing look case in NGC 1566
• Long-term IR Photometry of Seyferts
• 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
• The case for cases B and C: intrinsic hydrogen line ratios of the broad-line region of active galactic nuclei, reddenings, and accretion disc sizes
• Profile variability of the H-alpha and H-beta broad emission lines in NGC5548
• Multiple tidal disruption flares in the active galaxy IC 3599
• The detection and X-ray view of the changing look AGN HE 1136-2304
• Long-term optical spectral monitoring of a changing-look AGN NGC 3516 I: Continuum and broad-line flux variability
• Evidence for a receding dust sublimation region around a supermassive black hole
• 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
• Relativistic cross sections of mass stripping and tidal disruption of a star by a super-massive rotating black hole
• Broad Band X-Ray Spectra of Two Low-luminosity Active Galactic Nuclei NGC 1566 and NGC 4941
• NGC 1566: analysis of the nuclear region from optical and near-infrared Integral Field Unit spectroscopy
• The curtain remains open: NGC 2617 continues in a high state
• The analysis of the hydrogen broad Balmer line ratios: possible implications to the physical properties of the BLR of AGN
• Variability of the coronal line region in NGC 4151
• Strong variability of the coronal line region in NGC 5548
• Mechanism of the Changing Look phenomenon in Active Galactic Nuclei
• The dynamics of twisted disc formed after the tidal disruption of a star by a rotating black hole
• Tracing the AGN/X-ray Binary Analogy with Light Curves of Individual Changing-Look AGN
• 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
• PS1-13cbe: The Rapid "Turn on" of a Seyfert 1

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