Kavli Affiliate: Erin Kara
| First 5 Authors: Fatima Zaidouni, Erin Kara, Peter Kosec, Missagh Mehdipour, Daniele Rogantini
| Summary:
We present the results of the XMM-Newton and NuSTAR observations taken as
part of the ongoing, intensive multi-wavelength monitoring program of the
Seyfert 1 galaxy Mrk 817 by the AGN Space Telescope and Optical Reverberation
Mapping 2 (AGN STORM 2) Project. The campaign revealed an unexpected and
transient obscuring outflow, never before seen in this source. Of our four
XMM-Newton/NuSTAR epochs, one fortuitously taken during a bright X-ray state
has strong narrow absorption lines in the high-resolution grating spectra. From
these absorption features, we determine that the obscurer is in fact a
multi-phase ionized wind with an outflow velocity of $sim$5200 km s$^{-1}$,
and for the first time find evidence for a lower ionization component with the
same velocity observed in absorption features in the contemporaneous HST
spectra. This indicates that the UV absorption troughs may be due to dense
clumps embedded in diffuse, higher ionization gas responsible for the X-ray
absorption lines of the same velocity. We observe variability in the shape of
the absorption lines on timescales of hours, placing the variable component at
roughly 1000 $R_g$ if attributed to transverse motion along the line of sight.
This estimate aligns with independent UV measurements of the distance to the
obscurer suggesting an accretion disk wind at the inner broad line region. We
estimate that it takes roughly 200 days for the outflow to travel from the disk
to our line of sight, consistent with the timescale of the outflow’s column
density variations throughout the campaign.
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