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Active galactic nuclei (AGN) light curves observed with different wavebandsshow that the variability in longer wavelength bands lags the variability inshorter wavelength bands. Measuring these lags, or reverberation mapping, isused to measure the radial temperature profile and extent of AGN disks,typically with a reprocessing model that assumes X-rays are the main driver ofthe variability in other wavelength bands. To demonstrate how this reprocessingworks with realistic accretion disk structures, we use 3D local shearing boxmulti-frequency radiation magnetohydrodynamic (MHD) simulations to model theUV-emitting region of an AGN disk, which is unstable to the magnetorotationalinstability (MRI) and convection. At the same time, we inject hard X-rays($>1$~keV) into the simulation box to study the effects of X-ray irradiation onthe local properties of the turbulence and the resulting variability of theemitted UV light curve. We find that disk turbulence is sufficient to driveintrinsic variability in emitted UV light curves and that a damped random walk(DRW) model is a good fit to this UV light curve for timescales $>5$~days.Meanwhile, the injected X-rays have almost no impact on the power spectrum ofthe emitted UV light curve. In addition, the injected X-ray and emitted UVlight curves are only correlated if there is X-ray variability on timescales$>1$~day, in which case we find a correlation coefficient $r=0.52$. Theseresults suggest that hard X-rays with scattering dominated opacity are likelynot the main driver of the reverberation signals.

Simulating X-ray Reverberation in the UV-Emitting Regions of Active  Galactic Nuclei Accretion Disks with 3D Multi-Frequency Magnetohydrodynamic  Simulations