AGN STORM 2. III. A NICER view of the variable X-ray obscurer in Mrk 817

分类： 天文学 >> 天文学 提交时间： 2023-02-19

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 Bonta Maryam Dehghanian Pu Du Carina Fian

摘要： The AGN STORM 2 collaboration targeted the Seyfert 1 galaxy Mrk 817 for a year-long multiwavelength, coordinated reverberation mapping campaign including HST, Swift, XMM-Newton, NICER, and ground-based observatories. Early observations with NICER and XMM revealed an X-ray state ten 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 ($N_\mathrm{H}$ ranges from $2.85\substack{+0.48\\ -0.33} \times 10^{22}\text{ cm}^{-2}$ to $25.6\substack{+3.0\\ -3.5} \times 10^{22} \text{ cm}^{-2}$) 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.

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