AGN STORM 2. VI. Mapping Temperature Fluctuations in the Accretion Disk of Mrk 817

Jack M.M. Neustadt*, Christopher S. Kochanek, John Montano, Jonathan Gelbord, Aaron J. Barth, Gisella De Rosa, Gerard A. Kriss, Edward M. Cackett, Keith Horne, Erin A. Kara, Hermine Landt, Hagai Netzer, Nahum Arav, Misty C. Bentz, Elena Dalla Bontà, Maryam Dehghanian, Pu Du, Rick Edelson, Gary J. Ferland, Carina FianTravis Fischer, Michael R. Goad, Diego H. González Buitrago, Varoujan Gorjian, Catherine J. Grier, Patrick B. Hall, Y. Homayouni, Chen Hu, Dragana Ilić, Michael D. Joner, Jelle Kaastra, Shai Kaspi, Kirk T. Korista, Andjelka B. Kovačević, Collin Lewin, Yan Rong Li, Ian M. McHardy, Missagh Mehdipour, Jake A. Miller, Christos Panagiotou, Ethan Partington, Rachel Plesha, Richard W. Pogge, Luka Popović, Daniel Proga, Thaisa Storchi-Bergmann, David Sanmartim, Matthew R. Siebert, Matilde Signorini, Marianne Vestergaard, Fatima Zaidouni, Ying Zu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We fit the UV/optical lightcurves of the Seyfert 1 galaxy Mrk 817 to produce maps of the accretion disk temperature fluctuations δ T resolved in time and radius. The δ T maps are dominated by coherent radial structures that move slowly (v ≪ c) inward and outward, which conflicts with the idea that disk variability is driven only by reverberation. Instead, these slow-moving temperature fluctuations are likely due to variability intrinsic to the disk. We test how modifying the input lightcurves by smoothing and subtracting them changes the resulting δ T maps and find that most of the temperature fluctuations exist over relatively long timescales (hundreds of days). We show how detrending active galactic nucleus (AGN) lightcurves can be used to separate the flux variations driven by the slow-moving temperature fluctuations from those driven by reverberation. We also simulate contamination of the continuum emission from the disk by continuum emission from the broad-line region (BLR), which is expected to have spectral features localized in wavelength, such as the Balmer break contaminating the U band. We find that a disk with a smooth temperature profile cannot produce a signal localized in wavelength and that any BLR contamination should appear as residuals in our model lightcurves. Given the observed residuals, we estimate that only ∼20% of the variable flux in the U and u lightcurves can be due to BLR contamination. Finally, we discus how these maps not only describe the data but can make predictions about other aspects of AGN variability.

Original languageEnglish
Article number219
JournalAstrophysical Journal
Issue number2
StatePublished - 1 Feb 2024


FundersFunder number
Astronomical Observatory Belgrade451-03-68/2022-14/200002
Christopher R. Redlich FundGO-16196
National Science FoundationAST-2307385, AST-1814440, AST-1908570
National Science Foundation
National Aeronautics and Space AdministrationAST-1907290, 80NSSC22K0089, AST-1909199, 80NSSC22K1492
National Aeronautics and Space Administration
Alexander von Humboldt-Stiftung
University of Belgrade451-03-68/2022-14/200104
University of Belgrade
Space Telescope Science InstituteNAS5-26555
Space Telescope Science Institute
Science and Technology Facilities CouncilAST-2009230
Science and Technology Facilities Council
National Natural Science Foundation of China12273041, 11922304
National Natural Science Foundation of China
Chinese Academy of Sciences
Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja
Youth Innovation Promotion Association of the Chinese Academy of Sciences
Danmarks Frie ForskningsfondDFF 8021-00130
Danmarks Frie Forskningsfond


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