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

Homayouni, Y.; Kriss, Gerard A.; De Rosa, Gisella; Plesha, Rachel; Cackett, Edward M.; Goad, Michael R.; Korista, Kirk T.; 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; Dalla Bontà, Elena; Dehghanian, Maryam; Du, Pu; Ferland, Gary J.; 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, J. 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; Zu, Ying

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.

Citation

Homayouni, Y., Kriss, G. A., De Rosa, G., Plesha, R., Cackett, E. M., Goad, M. R., …Zu, Y. (2024). AGN STORM 2. V. Anomalous Behavior of the C iv Light Curve of Mrk 817. Astrophysical Journal, 963(2), Article 123. https://doi.org/10.3847/1538-4357/ad1be4

• Journal Article Type: Article
• Acceptance Date: Dec 27, 2023
• Online Publication Date: Mar 6, 2024
• Publication Date: 2024
• Deposit Date: May 21, 2024
• Publicly Available Date: May 21, 2024
• Journal: The Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 963
• Issue: 2
• Article Number: 123
• DOI: https://doi.org/10.3847/1538-4357/ad1be4
• Public URL: https://durham-repository.worktribe.com/output/2455460