AstroSat view of spectral transition in the changing-look active galaxy NGC1566 during the declining phase of the 2018 outburst

Abstract

NGC1566 is a changing-look active galaxy that exhibited an outburst during 2017-2018 with a peak in June 2018. We triggered AstroSat observations of NGC 1566 twice in August and October 2018 during its declining phase. Using the AstroSat observations along-with two XMM-Newton observations in 2015 (pre-outburst) and June 2018 (peak-outburst), we found that the X-ray power-law, the soft X-ray excess, and the disk components showed extreme variability during the outburst. Especially, the soft excess was negligible in 2015 before the outburst, it increased to a maximum level by a factor of $>200$ in June 2018, and reduced dramatically by a factor of $\sim 7.4$ in August 2018 and become undetectable in October 2018. The Eddington fraction ($L/L_{Edd})$ increased from $\sim 0.1\%$ (2015) to $\sim 5\%$ (June 2018), then decreased to $\sim 1.5\%$ (August 2018) and $0.3\%$ (October 2018). Thus, NGC 1566 made a spectral transition from a high soft-excess state to a negligible soft-excess state at a few $\%$ of the Eddington rate. The soft-excess is consistent with warm Comptonization in the inner disk that appears to have developed during the outburst and disappeared towards the end of the outburst over a timescale comparable to the sound crossing time. The multi-wavelength spectral evolution of NGC 1566 during the outburst is most likely caused by the radiation pressure instability in the inner regions of the accretion disk in NGC 1566.

arXiv commentAccepted for publication in ApJ, 18 pages, 8 figures, 3 tables

References in corpus (62)

• Astropy: A Community Python Package for Astronomy
• The chemical composition of the Sun
• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• AGN Black Hole Masses and Bolometric Luminosities
• Broad-band gamma-ray and X-ray spectra of NGC 4151 and their implications for physical processes and geometry
• The Relation Between Optical Extinction and Hydrogen Column Density in the Galaxy
• Intrinsic disc emission and the Soft X-ray Excess in AGN
• The May 1989 outburst of the Soft X-ray Transient GS 2023+338 (V404 Cyg)
• Sherpa: a Mission-Independent Data Analysis Application
• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• The GEMS project: X-ray analysis and statistical properties of the group sample
• A physical model of the broadband continuum of AGN and its implications for the UV/X relation and optical variability
• Changing look: from Compton-thick to Compton-thin, or the re-birth of fossil AGN
• Explaining changing-look AGN with state transition triggered by rapid mass accretion rate drop
• Discovery of 21 New Changing-look AGNs in Northern Sky
• In-orbit Calibrations of the Ultra-Violet Imaging Telescope
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• Calibration of the Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat
• Anatomy of the AGN in NGC 5548: I. A global model for the broadband spectral energy distribution
• ALMA observations of molecular tori around massive black holes
• High-Density Effects in X-ray Reflection Models from Accretion Disks
• Evolution of Broad-line Emission from Active Galactic Nuclei
• A Mid-IR Selected Changing-Look Quasar and Physical Scenarios for Abrupt AGN Fading
• Changing-Look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars
• The destruction and recreation of the X-ray corona in a changing-look Active Galactic Nucleus
• Towards an Understanding of Changing-Look Quasars: An Archival Spectroscopic Search in SDSS
• From Spitzer Galaxy Photometry to Tully-Fisher Distances
• Additional Calibration of the Ultra-Violet Imaging Telescope on board AstroSat
• Mid-infrared variability of changing-look AGN
• A possible mechanism for multiple changing look phenomenon in Active Galactic Nuclei
• High Density Reflection Spectroscopy: II. the Density of the Inner Black Hole Accretion Disc in AGN
• A new physical interpretation of optical and infrared variability in quasars
• The Analogous Structure of Accretion Flows in Supermassive and Stellar Mass Black Holes: New Insights from Faded Changing-Look Quasars
• Large Area X-ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its performance in the orbit
• New changing look case in NGC 1566
• A search for changing-look AGN in the Grossan catalog
• On different types of instabilities in black hole accretion discs. Implications for X-ray binaries and AGN
• The formerly X-ray reflection-dominated Seyfert~2 galaxy NGC6300
• Polarization of changing-look quasars
• The Black Hole Mass Function Derived from Local Spiral Galaxies
• The Changing-Look Quasar Mrk 590 is Awakening
• WALLABY Early Science - III. An HI Study of the Spiral Galaxy NGC 1566
• The nuclear gas disk of NGC 1566 dissected by SINFONI and ALMA
• The Lyman-alpha Forest and Heavy Element Systems of GB1759+7539
• Broad Band X-Ray Spectra of Two Low-luminosity Active Galactic Nuclei NGC 1566 and NGC 4941
• A high-density relativistic reflection origin for the soft and hard X-ray excess emission from Mrk 1044
• Two New "Turn-off" Changing-look Active Galactic nuclei and Implication on "Partially Obscured" AGNs
• Broadband X-Ray Observations of the 2018 Outburst of the Changing-Look Active Galactic Nucleus NGC 1566
• The post-maximum behaviour of the changing-look Seyfert galaxy NGC 1566
• Probing the nature and origin of dust in the reddened quasar IC 4329A with global modelling from X-ray to infrared
• Long-term monitoring of PKS0558-504 with Swift: the disc-corona link
• A Suzaku Observation of Mkn 590 Reveals a Vanishing Soft Excess
• In-orbit performance of AstroSat CZTI
• Hard X-ray Luminosity Function of Tidal Disruption Events: First Results from MAXI Extragalactic Survey
• Tidal Disruption of Stars by Supermassive Black Holes -- XMM-Newton Highlights and the Next Decade
• X-ray variability of AGN and correlations with spectral properties
• Calibration of AstroSat/UVIT Gratings and Spectral Responses
• Revealing Thermal Comptonization of accretion-disk photons in IC4329A with AstroSat
• In orbit performance of UVIT over the 5 years

Cited by in corpus (3)

• The origin of the vanishing soft X-ray excess in the changing-look Active Galactic Nucleus Mrk 590
• Comprehensive X-ray and Multiwavelength Study of ULXs in NGC 1566
• Thermal Comptonization in a changing corona in the changing-look active galaxy NGC 1566