AGN STORM 2. V. Anomalous Behavior of the C iv Light Curve of Mrk 817

Y. Homayouni, Gerard A. Kriss, Gisella De Rosa, Rachel Plesha, Edward M. Cackett, Michael R. Goad, Kirk T. Korista, Keith Horne, Travis Fischer, Tim Waters, Aaron J. Barth, Erin A. Kara, Hermine Landt, Nahum Arav, Benjamin D. Boizelle, Misty C. Bentz, Michael S. Brotherton, Doron Chelouche, Elena Dalla Bontà, Maryam DehghanianPu Du, Gary J. Ferland, Carina Fian, Jonathan Gelbord, Catherine J. Grier, Patrick B. Hall, Chen Hu, Dragana Ilić, Michael D. Joner, Jelle Kaastra, Shai Kaspi, Andjelka B. Kovačević, Daniel Kynoch, Yan Rong Li, Missagh Mehdipour, Jake A. Miller, Jake Mitchell, John Montano, Hagai Netzer, J. M.M. Neustadt, Ethan Partington, Luka Popović, Daniel Proga, Thaisa Storchi-Bergmann, David Sanmartim, Matthew R. Siebert, Tommaso Treu, Marianne Vestergaard, Jian Min Wang, Martin J. Ward, Fatima Zaidouni, Ying Zu

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


An intensive reverberation mapping campaign of the Seyfert 1 galaxy Mrk 817 using the Cosmic Origins Spectrograph on the Hubble Space Telescope revealed significant variations in the response of broad UV emission lines to fluctuations in the continuum emission. The response of the prominent UV emission lines changes over an ∼60 day duration, resulting in distinctly different time lags in the various segments of the light curve over the 14 month observing campaign. One-dimensional echo-mapping models fit these variations if a slowly varying background is included for each emission line. These variations are more evident in the C iv light curve, which is the line least affected by intrinsic absorption in Mrk 817 and least blended with neighboring emission lines. We identify five temporal windows with a distinct emission-line response, and measure their corresponding time delays, which range from 2 to 13 days. These temporal windows are plausibly linked to changes in the UV and X-ray obscuration occurring during these same intervals. The shortest time lags occur during periods with diminishing obscuration, whereas the longest lags occur during periods with rising obscuration. We propose that the obscuring outflow shields the broad UV lines from the ionizing continuum. The resulting change in the spectral energy distribution of the ionizing continuum, as seen by clouds at a range of distances from the nucleus, is responsible for the changes in the line response.

Original languageEnglish
Article number123
JournalAstrophysical Journal
Issue number2
StatePublished - 1 Mar 2024


FundersFunder number
Christopher R. Redlich Fund
Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja
Heising-Simons Foundation
Alexander von Humboldt-Stiftung
Gordon and Betty Moore Foundation
Astronomical Observatory Belgrade451-03-47/2023-01/200002
Chinese Academy of Sciences11991051, 11873048, NSFC-12022301
Chinese Academy of Sciences
Israel Science FoundationCH71-34-3, 2398/19
Israel Science Foundation
Space Telescope Science InstituteHST-AR-15018, NAS5-26555, HST-GO-16196.003-A
Space Telescope Science Institute
David and Lucile Packard Foundation1910687, 1816537, ATP 17-ATP17-0141, 19-ATP19-0188
David and Lucile Packard Foundation
NASA STScI HSTAR-16600, AR-15786, AR-16601, AR- 17556
Danmarks Frie ForskningsfondDFF 8021-00130
Danmarks Frie Forskningsfond
Natural Sciences and Engineering Research Council of Canada2017-05983
Natural Sciences and Engineering Research Council of Canada
Pennsylvania State UniversityAST-1907290, 80NSSC22K0089, AST 2106249, 80NSSC22K0570, 80NSSC21K1935, AST 1909199, GO1-22116X
Pennsylvania State University
National Aeronautics and Space AdministrationHST-GO-16196
National Aeronautics and Space Administration
Science and Technology Facilities CouncilAST-2009230, NSF-AST 1907208
Science and Technology Facilities Council
University of Belgrade451-03-47/2023-01/200104
University of Belgrade


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