Kavli Affiliate: Erin Kara
| First 5 Authors: Collin Lewin, Erin Kara, Edward M. Cackett, Dan Wilkins, Christos Panagiotou
| Summary:
UV and optical continuum reverberation mapping is powerful for probing the
accretion disk and inner broad-line region. However, recent reverberation
mapping campaigns in the X-ray, UV, and optical have found lags consistently
longer than those expected from the standard disk reprocessing picture. The
largest discrepancy to-date was recently reported in Mrk 335, where UV/optical
lags are up to 12 times longer than expected. Here, we perform a
frequency-resolved time lag analysis of Mrk 335, using Gaussian processes to
account for irregular sampling. For the first time, we compare the Fourier
frequency-resolved lags directly to those computed using the popular
Interpolated Cross-Correlation Function (ICCF) method applied to both the
original and detrended light curves. We show that the anticipated disk
reverberation lags are recovered by the Fourier lags when zeroing in on the
short-timescale variability. This suggests that a separate variability
component is present on long timescales. If this separate component is modeled
as reverberation from another region beyond the accretion disk, we constrain a
size-scale of roughly 15 light-days from the central black hole. This is
consistent with the size of the broad line region inferred from H$beta$
reverberation lags. We also find tentative evidence for a soft X-ray lag, which
we propose may be due to light travel time delays between the hard X-ray corona
and distant photoionized gas that dominates the soft X-ray spectrum below 2
keV.
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