Long-term optical, UV, and X-ray continuum variations in the changing-look AGN HE 1136-2304

Abstract

A strong outburst in the X-ray continuum and a change of its Seyfert spectral type was detected in HE 1136-2304 in 2014. The spectral type changed from nearly Seyfert 2 type (1.95) to Seyfert 1.5 type in comparison to previous observations taken ten to twenty years before. In a subsequent variability campaign we wanted to investigate whether this outburst was a single event or whether the variability pattern following the outburst was similar to those seen in other variable Seyfert galaxies. In addition to a SALT spectral variability campaign, we carried out optical continuum as well as X-ray and UV (Swift) monitoring studies from 2014 to 2017. HE 1136-2304 strongly varied on timescales of days to months from 2014 to 2017. No systematic trends were found in the variability behavior following the outburst in 2014. A general decrease in flux would have been expected for a tidal disruption event. This could not be confirmed. More likely the flux variations are connected to irregular fluctuations in the accretion rate. The strongest variability amplitudes have been found in the X-ray regime: HE 1136-2304 varied by a factor of eight during 2015. The amplitudes of the continuum variability (from the UV to the optical) systematically decreased with wavelength following a power law F_var = a $\times$ λ^-c with c = 0.84. There is a trend that the B-band continuum shows a delay of three light days with respect to the variable X-ray flux. The Seyfert type 1.5 did not change despite the strong continuum variations for the period between 2014 and 2017.

arXiv comment25 pages, 21 figures, Astronomy & Astrophysics in press

References in corpus (50)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• Correcting for the Effects of Interstellar Extinction
• The Swift X-ray Telescope
• The Swift Ultra-Violet/Optical Telescope
• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• A Cosmology Calculator for the World Wide Web
• Photometric Calibration of the Swift Ultraviolet/Optical Telescope
• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements II. The Full Sample of Reverberation-Mapped AGNs
• The 6dF Galaxy Survey: Samples, Observational Techniques and the First Data Release
• X-ray Spectral Variability and Rapid Variability of the Soft X-ray Spectrum Seyfert 1 Galaxies Ark 564 and Ton S180
• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• UBVRI Photometric Standard Stars Around the Celestial Equator: Updates and Additions
• Bayesian Estimation of Hardness Ratios: Modeling and Computations
• Six Months of Multi-Wavelength Follow-up of the Tidal Disruption Candidate ASASSN-14li and Implied TDE Rates from ASAS-SN
• A Systematic Search for Changing-Look Quasars in SDSS
• Space Telescope and Optical Reverberation Mapping Project. III. Optical Continuum Emission and Broad-Band Time Delays in NGC 5548
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• Testing thermal reprocessing in AGN accretion discs
• Optical Continuum and Emission-Line Variability of Seyfert 1 Galaxies
• The Simultaneous Optical-to-X-ray Spectral Energy Distribution of Soft X-ray Selected AGN observed by Swift
• UV/Optical Detections of Candidate Tidal Disruption Events by GALEX and CFHTLS
• Paper II: Calibration of the Swift ultraviolet/optical telescope
• The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves
• Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A Thirteen-Year Study of Spectral Variability in NGC 5548
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei. IV. Effects of Compton Scattering and Metal Opacities
• Evolution of Broad-line Emission from Active Galactic Nuclei
• Accretion disk wind in the AGN broad-line region: Spectroscopically resolved line profile variations in Mrk110
• Discovery of superstrong, fading, iron line emission and double-peaked Balmer lines of the galaxy SDSSJ0952+2143 - the light echo of a huge flare
• The First Swift Ultra-Violet/Optical Telescope GRB Afterglow Catalog
• Optical atmospheric extinction over Cerro Paranal
• Space Telescope and Optical Reverberation Mapping Project. V. Optical Spectroscopic Campaign and Emission-Line Analysis for NGC 5548
• X-ray variability in a complete sample of Soft X-ray selected AGN
• Photometric AGN reverberation mapping - an efficient tool for BLR sizes, black hole masses and host-subtracted AGN luminosities
• Spectral Optical Monitoring of the Narrow Line Seyfert 1 galaxy Ark 564
• Long-Term Optical Continuum Color Variability of Nearby Active Galactic Nuclei
• The detection and X-ray view of the changing look AGN HE 1136-2304
• Short-term emission line and continuum variations in Mrk110
• The formerly X-ray reflection-dominated Seyfert~2 galaxy NGC6300
• Spectral optical monitoring of 3C390.3 in 1995-2007: I. Light curves and flux variation of the continuum and broad lines
• Broad-line region structure and kinematics in the radio galaxy 3C 120
• The broad-line region and dust torus size of the Seyfert 1 galaxy PGC50427
• Broad-line region structure and line profile variations in the changing look AGN HE1136-2304
• Periodic variable stars in CoRoT field LRa02 observed with BEST II
• Line profile and continuum variability in the very broad-line Seyfert galaxy Mrk 926
• Spectral analysis of four 'hypervariable' AGN: a microneedle in the haystack?
• The stability of the optical flux variation gradient for 3C120

Cited by in corpus (18)

• Magnetic flux inversion in a peculiar changing look AGN
• Reverberation Mapping of Changing-look Active Galactic Nucleus NGC 3516
• MUSE observations of a changing-look AGN I: The re-appearance of the broad emission lines
• Multi-Wavelength Monitoring and Reverberation Mapping of a Changing Look Event in the Seyfert Galaxy NGC 3516
• Broad-line region structure and line profile variations in the changing look AGN HE1136-2304
• HST/COS observations of the newly discovered obscuring outflow in NGC 3783
• A forward modelling approach to AGN variability -- Method description and early applications
• Investigating Changing-Look Active Galactic Nuclei with Long-term Optical and X-Ray Observations
• Optical and X-ray discovery of the changing-look AGN IRAS23226-3843 showing extremely broad and double-peaked Balmer profiles
• Constraining the X-ray reflection in low accretion rate AGN using XMM-Newton, NuSTAR and Swift
• The transient event in NGC 1566 from 2017 to 2019 -- I. An eccentric accretion disk and a turbulent, disk-dominated broad-line region unveiled by double-peaked Ca II and O I lines
• Merging cold front and AGN feedback in the peculiar galaxy cluster Abell 2626
• The outburst of the changing-look AGN IRAS23226-3843 in 2019
• A Systematic Survey for z < 0.04 Changing-Look AGNs
• The Great Slump: Mrk926 reveals discrete and varying Balmer line satellite components during a drastic phase of decline
• Changing Look AGN: A study of Optical/UV and the Highly Ionized Fe K$\alpha$ X-ray Line Flux Variations Using Photo-Ionization Simulations
• A radio, optical, UV and X-ray view of the enigmatic changing look Active Galactic Nucleus 1ES~1927+654 from its pre- to post-flare states
• Low-Eddington ratio, changing-look active galactic nuclei: the case of NGC 4614