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

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

Abstract

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.

Citation

Neustadt, J. M. M., Kochanek, C. S., Montano, J., Gelbord, J., Barth, A. J., De Rosa, G., …Zu, Y. (2024). AGN STORM 2. VI. Mapping Temperature Fluctuations in the Accretion Disk of Mrk 817. Astrophysical Journal, 961(2), Article 219. https://doi.org/10.3847/1538-4357/ad1386

• Journal Article Type: Article
• Acceptance Date: Dec 6, 2023
• Online Publication Date: Jan 29, 2024
• Publication Date: Feb 1, 2024
• Deposit Date: Mar 19, 2024
• Publicly Available Date: Mar 19, 2024
• Journal: The Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 961
• Issue: 2
• Article Number: 219
• DOI: https://doi.org/10.3847/1538-4357/ad1386
• Public URL: https://durham-repository.worktribe.com/output/2192880