Kavli Affiliate: Erin Kara
| First 5 Authors: Collin Lewin, Erin Kara, Aaron J. Barth, Edward M. Cackett, Gisella De Rosa
| Summary:
X-ray reverberation mapping is a powerful technique for probing the innermost
accretion disk, whereas continuum reverberation mapping in the UV, optical, and
infrared (UVOIR) reveals reprocessing by the rest of the accretion disk and
broad-line region (BLR). We present the time lags of Mrk 817 as a function of
temporal frequency measured from 14 months of high-cadence monitoring from
Swift and ground-based telescopes, in addition to an XMM-Newton observation, as
part of the AGN STORM 2 campaign. The XMM-Newton lags reveal the first
detection of a soft lag in this source, consistent with reverberation from the
innermost accretion flow. These results mark the first simultaneous measurement
of X-ray reverberation and UVOIR disk reprocessing
lags$unicode{x2013}$effectively allowing us to map the entire accretion disk
surrounding the black hole. Similar to previous continuum reverberation mapping
campaigns, the UVOIR time lags arising at low temporal frequencies are longer
than those expected from standard disk reprocessing by a factor of 2-3. The
lags agree with the anticipated disk reverberation lags when isolating
short-timescale variability, namely timescales shorter than the H$beta$ lag.
Modeling the lags requires additional reprocessing constrained at a radius
consistent with the BLR size scale inferred from contemporaneous H$beta$-lag
measurements. When we divide the campaign light curves, the UVOIR lags show
substantial variations, with longer lags measured when obscuration from an
ionized outflow is greatest. We suggest that, when the obscurer is strongest,
reprocessing by the BLR elongates the lags most significantly. As the wind
weakens, the lags are dominated by shorter accretion disk lags.
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