AGN STORM 2. I. First results: a change in the weather of Mrk 817

E. Kara, M. Mehdipour, G.A. Kriss, E.M. Cackett, N. Arav, A.J. Barth, D. Byun, M.S. Brotherton, G. De Rosa, J. Gelbord, J.V. Hernández Santisteban, C. Hu, J. Kaastra, H. Landt, Y.-R. Li, J.A. Miller, J. Montano, E. Partington, J. Aceituno, J.-M. BaiD. Bao, M.C. Bentz, T.G. Brink, D. Chelouche, Y.-J. Chen, E.R. Colmenero, E. Dalla Bontà, M. Dehghanian, P. Du, R. Edelson, G.J. Ferland, L. Ferrarese, C. Fian, A.V. Filippenko, T. Fischer, M.R. Goad, D.H. González Buitrago, V. Gorjian, C.J. Grier, W.-J. Guo, P.B. Hall, L.C. Ho, Y. Homayouni, K. Horne, D. Ilić, B.-W. Jiang, M.D. Joner, S. Kaspi, C.S. Kochanek, K.T. Korista, D. Kynoch, S.-S. Li, J.-R. Liu, I.M. M. Chardy, J.N. McLane, J.A.J. Mitchell, H. Netzer, K.A. Olson, R.W. Pogge, L.C. Popović, D. Proga, T. Storchi-Bergmann, E. Strasburger, T. Treu, M. Vestergaard, J.-M. Wang, M.J. Ward, T. Waters, P.R. Williams, S. Yang, Z.-H. Yao, T.E. Zastrocky, S. Zhai, Y. Zu

Research output: Contribution to journalArticlepeer-review


We present the first results from the ongoing, intensive, multiwavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this active galactic nucleus was, in part, selected for its historically unobscured nature, we discovered that the X-ray spectrum is highly absorbed, and there are new blueshifted, broad, and narrow UV absorption lines, which suggest that a dust-free, ionized obscurer located at the inner broad-line region partially covers the central source. Despite the obscuration, we measure UV and optical continuum reverberation lags consistent with a centrally illuminated Shakura-Sunyaev thin accretion disk, and measure reverberation lags associated with the optical broad-line region, as expected. However, in the first 55 days of the campaign, when the obscuration was becoming most extreme, we observe a de-coupling of the UV continuum and the UV broad emission-line variability. The correlation recovered in the next 42 days of the campaign, as Mrk 817 entered a less obscured state. The short C iv and Lyα lags suggest that the accretion disk extends beyond the UV broad-line region. © 2021. The American Astronomical Society. All rights reserved..
Original languageEnglish
Article number151
Number of pages21
JournalAstrophysical Journal
Issue number2
Early online date26 Nov 2021
Publication statusPublished - 1 Dec 2021


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