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AGN STORM 2. II. Ultraviolet Observations of Mrk 817 with the Cosmic Origins Spectrograph on the Hubble Space Telescope*

Homayouni, Y.; De Rosa, Gisella; Plesha, Rachel; Kriss, Gerard A.; Barth, Aaron J.; Cackett, Edward M.; Horne, Keith; Kara, Erin A.; Landt, Hermine; Arav, Nahum; Boizelle, Benjamin D.; Bentz, Misty C.; Brink, Thomas G.; Brotherton, Michael S.; Chelouche, Doron; Dalla Bontà, Elena; Dehghanian, Maryam; Du, Pu; Ferland, Gary J.; Ferrarese, Laura; Fian, Carina; Filippenko, Alexei V.; Fischer, Travis; Foley, Ryan J.; Gelbord, Jonathan; Goad, Michael R.; González Buitrago, Diego H.; Gorjian, Varoujan; Grier, Catherine J.; Hall, Patrick B.; Hernández Santisteban, Juan V.; Hu, Chen; Ilić, Dragana; Joner, Michael D.; Kaastra, Jelle; Kaspi, Shai; Kochanek, Christopher S.; Korista, Kirk T.; Kovačević, Andjelka B.; Kynoch, Daniel; Li, Yan-Rong; McHardy, Ian M.; McLane, Jacob N.; Mehdipour, Missagh; Miller, Jake A.; Mitchell, Jake; Montano, John; Netzer, Hagai; Panagiotou, Christos; Partington, Ethan; Pogge, Richard W.; Č. Popović, Luka; Proga, Daniel; Rogantini, Daniele; Storchi-Bergmann, Thaisa;...

AGN STORM 2. II. Ultraviolet Observations of Mrk 817 with the Cosmic Origins Spectrograph on the Hubble Space Telescope* Thumbnail


Y. Homayouni

Gisella De Rosa

Rachel Plesha

Gerard A. Kriss

Aaron J. Barth

Edward M. Cackett

Keith Horne

Erin A. Kara

Nahum Arav

Benjamin D. Boizelle

Misty C. Bentz

Thomas G. Brink

Michael S. Brotherton

Doron Chelouche

Elena Dalla Bontà

Maryam Dehghanian

Pu Du

Gary J. Ferland

Laura Ferrarese

Carina Fian

Alexei V. Filippenko

Travis Fischer

Ryan J. Foley

Jonathan Gelbord

Michael R. Goad

Diego H. González Buitrago

Varoujan Gorjian

Catherine J. Grier

Patrick B. Hall

Juan V. Hernández Santisteban

Chen Hu

Dragana Ilić

Michael D. Joner

Jelle Kaastra

Shai Kaspi

Christopher S. Kochanek

Kirk T. Korista

Andjelka B. Kovačević

Daniel Kynoch

Yan-Rong Li

Ian M. McHardy

Jacob N. McLane

Missagh Mehdipour

Jake A. Miller

Jake Mitchell

John Montano

Hagai Netzer

Christos Panagiotou

Ethan Partington

Richard W. Pogge

Luka Č. Popović

Daniel Proga

Daniele Rogantini

Thaisa Storchi-Bergmann

David Sanmartim

Matthew R. Siebert

Tommaso Treu

Marianne Vestergaard

Jian-Min Wang

Tim Waters

Peter R. Williams

Fatima Zaidouni

Ying Zu


We present reverberation mapping measurements for the prominent ultraviolet broad emission lines of the active galactic nucleus Mrk 817 using 165 spectra obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our ultraviolet observations are accompanied by X-ray, optical, and near-infrared observations as part of the AGN Space Telescope and Optical Reverberation Mapping Program 2 (AGN STORM 2). Using the cross-correlation lag analysis method, we find significant correlated variations in the continuum and emission-line light curves. We measure rest-frame delayed responses between the far-ultraviolet continuum at 1180 Å and Lyαλ1215 Å (${10.4}_{-1.4}^{+1.6}$ days), N vλ1240 Å (${15.5}_{-4.8}^{+1.0}$ days), Si iv + ]O ivλ1397 Å (${8.2}_{-1.4}^{+1.4}$ days), C ivλ1549 Å (${11.8}_{-2.8}^{+3.0}$ days), and He iiλ1640 Å (${9.0}_{-1.9}^{+4.5}$ days) using segments of the emission-line profile that are unaffected by absorption and blending, which results in sampling different velocity ranges for each line. However, we find that the emission-line responses to continuum variations are more complex than a simple smoothed, shifted, and scaled version of the continuum light curve. We also measure velocity-resolved lags for the Lyα and C iv emission lines. The lag profile in the blue wing of Lyα is consistent with virial motion, with longer lags dominating at lower velocities, and shorter lags at higher velocities. The C iv lag profile shows the signature of a thick rotating disk, with the shortest lags in the wings, local peaks at ±1500 km s−1, and a local minimum at the line center. The other emission lines are dominated by broad absorption lines and blending with adjacent emission lines. These require detailed models, and will be presented in future work.


Homayouni, Y., De Rosa, G., Plesha, R., Kriss, G. A., Barth, A. J., Cackett, E. M., …Zu, Y. (2023). AGN STORM 2. II. Ultraviolet Observations of Mrk 817 with the Cosmic Origins Spectrograph on the Hubble Space Telescope*. Astrophysical Journal, 948(2), Article 85.

Journal Article Type Article
Acceptance Date Mar 11, 2023
Online Publication Date May 10, 2023
Publication Date May 10, 2023
Deposit Date May 24, 2023
Publicly Available Date May 24, 2023
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 948
Issue 2
Article Number 85
Public URL


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Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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