Abstract
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.
Document Type
Article
Publication Date
2024
Digital Object Identifier (DOI)
https://doi.org/10.3847/1538-4357/ad1be4
Funding Information
This paper is the fifth in a planned series of papers by the AGN STORM 2STORM 2 collaboration. 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. We are grateful to the dedication of the Institute staff who worked hard to review and implement this program. We particularly thank the Program Coordinator, W. Januszewski, who made sure the intensive monitoring schedule and coordination with other facilities continued successfully. Y.H. acknowledges support from NASA grant HST-GO- 16196, and was also supported as an Eberly Research Fellow by the Eberly College of Science at the Pennsylvania State University. Research at UC Irvine has been supported by NSF grant AST-1907290. Research at Wayne State University was supported by NSF grant AST 1909199, and NASA grants 80NSSC21K1935 and 80NSSC22K0089. E.K. acknowledges support from NASA grants 80NSSC22K0570 and GO1- 22116X. N.A. acknowledges support from NSF grant AST 2106249, as well as NASA STScI HST grants AR-15786, AR- 16600, AR-16601, and AR- 17556. 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. T.T. and P.R.W. acknowledge support by NASA through grant HST-GO-16196, by NSF through grant NSF- AST 1907208, and by the Packard Foundation through a Packard Research Fellowship to T.T. G.J.F. and M.D. acknowledge support by NSF (1816537 and 1910687), NASA (ATP 17-ATP17-0141 and 19-ATP19-0188), and STScI (HST- AR-15018 and HST-GO-16196.003-A). P.B.H. is supported by NSERC grant 2017-05983. M.V. gratefully acknowledges financial support from the Independent Research Fund Denmark via grant number DFF 8021-00130. D.H.G.B. acknowledges CONACYT support #319800 and of the researchers program for Mexico. D.C. acknowledges support by the ISF (2398/19) and the D.F.G. (CH71-34-3). A.V.F. was supported by the U.C. Berkeley Miller Institute of Basic Research in Science (where he was a Miller Senior Fellow), the Christopher R. Redlich Fund, and numerous individual donors. The UCSC team is supported in part by the Gordon and Betty Moore Foundation, the Heising-Simons Foundation, and by a fellowship from the David and Lucile Packard Foundation to R.J.F. D.I., A.B.K., and L.Č.P. acknowledge funding provided by the University of Belgrade–Faculty of Mathematics (contract No. 451-03-47/2023-01/200104) and Astronomical Observatory Belgrade (contract No. 451-03-47/2023-01/200002) through grants from the Ministry of Science, Technological Development and Innovation of the Republic of Serbia. D.I. acknowledges the support of the Alexander von Humboldt Foundation. A.B.K. and L.Č.P. thank the support of the Chinese Academy of Sciences Presidentʼs International Fellowship Initiative (PIFI) for visiting scientists. P.D. acknowledges financial support from NSFC grants NSFC-12022301, 11873048, and 11991051.
Repository Citation
Homayouni, Y.; Kriss, Gerard A.; De Rosa, Gisella; Plesha, Rachel; Cackett, Edward M.; Goad, Michael R.; Korista, Kirk; Horne, Keith; Fischer, Travis; Waters, Tim; Barth, Aaron J.; Kara, Erin A.; Landt, Hermine; Arav, Nahum; Boizelle, Benjamin D.; Bentz, Misty C.; Brotherton, Michael S.; Chelouche, Doron; Bontà, Elena Dalla; Dehghanian, Maryam; Du, Pu; Ferland, Gary; Fian, Carina; Gelbord, Jonathan; Grier, Catherine J.; Hall, Patrick B.; Hu, Chen; Ilić, Dragana; Joner, Michael D.; Kaastra, Jelle; Kaspi, Shai; Kovačević, Andjelka B.; Kynoch, Daniel; Li, Yan-Rong; Mehdipour, Missagh; Miller, Jake A.; Mitchell, Jake; Montano, John; Netzer, Hagai; Neustadt, Jack M. M.; Partington, Ethan; Popović, Luka Č.; Proga, Daniel; Storchi-Bergmann, Thaisa; Sanmartim, David; Siebert, Matthew R.; Treu, Tommaso; Vestergaard, Marianne; Wang, Jian-Min; Ward, Martin J.; Zaidouni, Fatima; and Zu, Ying, "AGN STORM 2. V. Anomalous Behavior of the C IV Light Curve of Mrk 817" (2024). Physics and Astronomy Faculty Publications. 685.
https://uknowledge.uky.edu/physastron_facpub/685
Notes/Citation Information
© 2024. The Author(s). Published by the American Astronomical Society.