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Space Telescope and Optical Reverberation Mapping Project 2: Variations of the UV Absorption Lines in Mrk 817

Presentation #104.02 in the session “AGN STORM 2: initial results from this large, multi-wavelength reverberation mapping campaign on Mrk 817”.

Published onApr 01, 2022
Space Telescope and Optical Reverberation Mapping Project 2: Variations of the UV Absorption Lines in Mrk 817

Our year-long campaign of monitoring the Seyfert 1 galaxy Mrk 817 has revealed it to be in an unusually bright state accompanied by new, unexpectedly strong absorption at both ultraviolet and X-ray wavelengths. The new UV absorption features comprise broad and narrow troughs, both having fairly high outflow velocities. The broad troughs, with widths of ~1000 km/s, are blue-shifted at -5300 to -6000 km/s; the narrow troughs, with widths of ~180 km/s, have blue shifts of -3700 km/s and lie at the red end of the broad absorption troughs. The absorption is highly variable and correlated with the soft X-ray obscuration. When the UV absorption is strongest, additional broad absorption appears, extending to blue shifts of -11,500 km/s. The absorbing gas has high ionization, exemplified by the strong troughs of O VI and S VI, high density (> 1e9 cm-3) as measured by absorption in the excited, metastable lines of the C III* multiplet at 1176 A, and high column density, measured by the saturated lines of the Lyman series as well as the presence of strong P V absorption. Photoionization modeling shows that the gas lies near the inner edge of the broad-line region, and is illuminated by an ionizing continuum filtered by the gas obscuring the soft X-ray emission. While the narrow absorption features exhibit a photoionization response to variations in the continuum brightness, the broad features do not. The broad UV absorption and the X-ray obscuration may be related to variations in the accretion flow resulting in an outflowing wind driven off the accretion disk. We will discuss this interpretation in relation to obscuring events observed in other AGN.

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