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AGN STORM 2. III. A NICER View of the Variable X-Ray Obscurer in Mrk 817

Partington, Ethan R.; Cackett, Edward M.; Kara, Erin; Kriss, Gerard A.; Barth, Aaron J.; De Rosa, Gisella; Homayouni, Y.; Horne, Keith; Landt, Hermine; Zoghbi, Abderahmen; Edelson, Rick; Arav, Nahum; Boizelle, Benjamin D.; Bentz, Misty C.; Brotherton, Michael S.; Byun, Doyee; Dalla Bontà, Elena; Dehghanian, Maryam; Du, Pu; Fian, Carina; Filippenko, Alexei V.; Gelbord, Jonathan; Goad, Michael R.; González Buitrago, Diego H.; Grier, Catherine J.; Hall, Patrick B.; Hu, Chen; Ilić, Dragana; Joner, Michael D.; Kaspi, Shai; Kochanek, Christopher S.; Korista, Kirk T.; Kovačević, Andjelka B.; Kynoch, Daniel; McLane, Jacob N.; Mehdipour, Missagh; Miller, Jake A.; Panagiotou, Christos; Plesha, Rachel; Č. Popović, Luka; Proga, Daniel; Rogantini, Daniele; Storchi-Bergmann, Thaisa; Sanmartim, David; Siebert, Matthew R.; Vestergaard, Marianne; Ward, Martin J.; Waters, Tim; Zaidouni, Fatima

AGN STORM 2. III. A NICER View of the Variable X-Ray Obscurer in Mrk 817 Thumbnail


Ethan R. Partington

Edward M. Cackett

Erin Kara

Gerard A. Kriss

Aaron J. Barth

Gisella De Rosa

Y. Homayouni

Keith Horne

Abderahmen Zoghbi

Rick Edelson

Nahum Arav

Benjamin D. Boizelle

Misty C. Bentz

Michael S. Brotherton

Doyee Byun

Elena Dalla Bontà

Maryam Dehghanian

Pu Du

Carina Fian

Alexei V. Filippenko

Jonathan Gelbord

Michael R. Goad

Diego H. González Buitrago

Catherine J. Grier

Patrick B. Hall

Chen Hu

Dragana Ilić

Michael D. Joner

Shai Kaspi

Christopher S. Kochanek

Kirk T. Korista

Andjelka B. Kovačević

Daniel Kynoch

Jacob N. McLane

Missagh Mehdipour

Jake A. Miller

Christos Panagiotou

Rachel Plesha

Luka Č. Popović

Daniel Proga

Daniele Rogantini

Thaisa Storchi-Bergmann

David Sanmartim

Matthew R. Siebert

Marianne Vestergaard

Martin J. Ward

Tim Waters

Fatima Zaidouni


The AGN STORM 2 Collaboration targeted the Seyfert 1 galaxy Mrk 817 for a year-long multiwavelength, coordinated reverberation mapping campaign including Hubble Space Telescope, Swift, XMM-Newton, NICER, and ground-based observatories. Early observations with NICER and XMM revealed an X-ray state 10 times fainter than historical observations, consistent with the presence of a new dust-free, ionized obscurer. The following analysis of NICER spectra attributes variability in the observed X-ray flux to changes in both the column density of the obscurer by at least one order of magnitude (NH ranges from ${2.85}_{-0.33}^{+0.48}\times {10}^{22}\,{\mathrm{cm}}^{-2}$ to ${25.6}_{-3.5}^{+3.0}\times {10}^{22}\,{\mathrm{cm}}^{-2}$) and the intrinsic continuum brightness (the unobscured flux ranges from 10−11.8 to 10−10.5 erg s−1 cm−2). While the X-ray flux generally remains in a faint state, there is one large flare during which Mrk 817 returns to its historical mean flux. The obscuring gas is still present at lower column density during the flare, but it also becomes highly ionized, increasing its transparency. Correlation between the column density of the X-ray obscurer and the strength of UV broad absorption lines suggests that the X-ray and UV continua are both affected by the same obscuration, consistent with a clumpy disk wind launched from the inner broad-line region.


Partington, E. R., Cackett, E. M., Kara, E., Kriss, G. A., Barth, A. J., De Rosa, G., …Zaidouni, F. (2023). AGN STORM 2. III. A NICER View of the Variable X-Ray Obscurer in Mrk 817. Astrophysical Journal, 947(1), Article 2.

Journal Article Type Article
Acceptance Date Feb 24, 2023
Online Publication Date Apr 10, 2023
Publication Date Apr 10, 2023
Deposit Date May 30, 2023
Publicly Available Date May 30, 2023
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 947
Issue 1
Article Number 2
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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