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

Ethan R. Partington, Edward M. Cackett, Erin Kara, Gerard A. Kriss, Aaron J. Barth, Gisella De Rosa, Y. Homayouni, Keith Horne, Hermine Landt, 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 FianAlexei 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

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


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 (N H ranges from 2.85 − 0.33 + 0.48 × 10 22 cm − 2 to 25.6 − 3.5 + 3.0 × 10 22 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.

Original languageEnglish (US)
Article number2
JournalAstrophysical Journal
Issue number1
StatePublished - Apr 1 2023
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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