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

Abstract

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.

Citation

Partington, E. R., Cackett, E. M., Kara, E., Kriss, G. A., Barth, A. J., De Rosa, G., Homayouni, Y., Horne, K., Landt, H., Zoghbi, A., Edelson, R., Arav, N., Boizelle, B. D., Bentz, M. C., Brotherton, M. S., Byun, D., Dalla Bontà, E., Dehghanian, M., Du, P., Fian, C., …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. https://doi.org/10.3847/1538-4357/acbf44

• 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
• DOI: https://doi.org/10.3847/1538-4357/acbf44
• Public URL: https://durham-repository.worktribe.com/output/1172450