AGN STORM 2: X. The origin of the interband continuum delays in Mrk 817

Kavli Affiliate: Erin Kara

| First 5 Authors: Hagai Netzer, Michael R. Goad, Aaron J. Barth, Edward M. Cackett, Keith Horne

| Summary:

The local (z=0.0315) AGN Mrk 817, was monitored over more than 500 days with
space-borne and ground-based instruments as part of a large international
campaign AGN STORM 2. Here, we present a comprehensive analysis of the
broad-band continuum variations using detailed modeling of the broad line
region (BLR), several types of disk winds classified by their optical depth,
and new numerical simulations. We find that diffuse continuum (DC) emission,
with additional contributions from strong and broad emission lines, can explain
the continuum lags observed in this source during high and low luminosity
phases. Disk illumination by the variable X-ray corona contributes only a small
fraction of the observed continuum lags. Our BLR models assume radiation
pressure-confined clouds distributed over a distance of 2-122 light days. We
present calculated mean-emissivity radii of many emission lines, and DC
emission, and suggest a simple, transfer-function-dependent method that ties
them to cross-correlation lag determinations. We do not find clear indications
for large optical depth winds but identify the signature of lower column
density winds. In particular, we associate the shortest observed continuum lags
with a combination of tau(1 Ryd) approx. 2 wind and a partly shielded BLR. Even
smaller optical depth winds may be associated with X-ray absorption features
and with noticeable variations in the width and lags of several high ionization
lines like HeII and CIV. Finally, we demonstrate the effect of torus dust
emission on the observed lags in the i and z bands.

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