Abstract
We fit the UV/optical lightcurves of the Seyfert 1 galaxy Mrk 817 to produce maps of the accretion disk temperature fluctuations δT resolved in time and radius. The δT 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 δT 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.
Document Type
Article
Publication Date
2024
Digital Object Identifier (DOI)
https://doi.org/10.3847/1538-4357/ad1386
Funding Information
Our project began with the successful Cycle 28 HST proposal 16196 (Peterson et al. 2020). Support for Hubble Space Telescope program GO-16196 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5- 26555. Figure 17. Top: Swift XRT 0.3–10 keV lightcurve in observed counts. Center: temperature map (ξ = 10). Note that the y-axis has been inverted (inner radii are at the top, outer at the bottom) compared to earlier figures. Bottom: Swift UVW2 lightcurve (black) and model fits (red). Dashed black lines correspond to noticeable features in the X-ray and UV lightcurves. The pink and cyan lines in the temperature map seem to correspond to similar structures in the X-ray and UV lightcurves, respectively. J.M.M.N. thanks Z. Yu and N. Downing for assistance with JAVELIN . J.M.M.N. and C.S.K. are supported by NSF grants AST-1814440 and AST-1908570. C.S.K. is supported by NSF grant AST-2307385. J.G. gratefully acknowledges support from NASA through grant 80NSSC22K1492. Research at UC Irvine was supported by NSF grant AST-1907290. E.M.C. gratefully acknowledges support from NASA through grant 80NSSC22K0089 and support from the NSF through grant No. AST-1909199. H.L. acknowledges a Daphne Jackson Fellowship sponsored by the Science and Technology Facilities Council (STFC), UK. M.C.B. gratefully acknowledges support from the NSF through grant AST-2009230. A.V.F. is grateful for financial assistance from the Christopher R. Redlich Fund and numerous individual donors. Y.H. was supported as an Eberly Research Fellow by the Eberly College of Science at the Pennsylvania State University. Y.H. acknowledges support from the Hubble Space Telescope program GO-16196, provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. D.I., A.B.K, and L.Č.P. acknowledge funding provided by the University of Belgrade—Faculty of Mathematics (contract 451-03-68/2022-14/200104), Astronomical Observatory Belgrade (contract 451-03-68/2022-14/ 200002), through grants by the Ministry of Education, Science, and Technological Development of the Republic of Serbia. D.I. acknowledges the support of the Alexander von Humboldt Foundation. A.B.K. and L.Č.P. are thankful for the support of the Chinese Academy of Sciences President’s International Fellowship Initiative (PIFI) for visiting scientist. Y.R.L. acknowledges financial support from NSFC through grant Nos. 11922304 and 12273041 and from the Youth Innovation Promotion Association CAS. M.R.S. is supported by the STScI Postdoctoral Fellowship. M.V. gratefully acknowledges support from the Independent Research Fund Denmark via grant No. DFF 8021-00130. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.
Repository Citation
Neustadt, Jack M. M.; Kochanek, Christopher S.; Montano, John; Gelbord, Jonathan M.; 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.; Bontà, Elena Dalla; Dehghanian, Maryam; Du, Pu; Edelson, Rick; Ferland, Gary; Fian, Carina; Fischer, Travis; Goad, Michael R.; González Buitrago, Diego H.; Gorjian, Varoujan; Grier, Catherine J.; Hall, Patrick B.; Homayouni, Yasaman; 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.; and Signorini, Matilde, "AGN STORM 2. VI. Mapping Temperature Fluctuations in the Accretion Disk of Mrk 817" (2024). Physics and Astronomy Faculty Publications. 686.
https://uknowledge.uky.edu/physastron_facpub/686
Notes/Citation Information
© 2024. The Author(s). Published by the American Astronomical Society.