Kavli Affiliate: Erin Kara
| First 5 Authors: Scott Hagen, Scott Hagen, , ,
| Summary:
The accretion flow in AGN is not well understood, motivating intensive
monitoring campaigns of multiwavelength variability to probe its structure. One
of the best of these is the 3 year optical/UV/X-ray approximately daily
monitoring campaign on Fairall,9, a fairly typical moderate accretion rate
AGN. The UV lightcurve shows a clear increase over $sim 50$ days between years
1 and 2, strongly coherent with the X-ray lightcurve rise. This changes the
average spectral energy distribution such that the disc component is stronger
while the X-ray spectrum steepens, so that the total X-ray power remains
roughly constant. Outside of this global change, we apply a Fourier resolved
analysis to test stochastic models where intrinsic fluctuations in the UV disc
propagate down into the hard X-ray emission region via both changing the seed
photon flux for Compton scattering (short light travel timescale) and changing
the electron density (longer propagation timescale). Unlike these models, the
hard X-rays are not particularly well correlated with the UV, and also have the
wrong sign in that the hard X-rays marginally lead the UV fluctuations. We show
that this is instead consistent with uncorrelated stochastic fluctuations in
both the UV (slow) and X-ray (fast), which are linked together only weakly via
light travel time. These variability properties, as well as the changes in the
SED, has implications for our understanding of AGN structure and physics, as
well as future monitoring campaigns.
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