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A.J. Berkeley (UMD), D. Kazanas (NASA/GSFC), J. Ozik (UMD)
We model the correlated X-ray -- UV observations of NGC 7469, for which well sampled data in both these bands have been obtained recently by a multiwavelength monitoring campaign. To this end we derive the response function for reprocessing hard (X-ray) to UV radiation from a point source by an infinite plane, located at a given distance below the source, as a function of the wavelength \lambda of the reprocessed radiation and the time lag \tau, under the assumption that the X-ray flux is reprocessed and emitted locally as a black body of the appropriate temperature. Using the observed X-ray light curve as input we compute the expected continuum UV emission as a function of time at wavelengths \lambda \lambda 1360 Å~ and \lambda \lambda 4690 Å, assuming that the the X-ray source is located a few Schwarzschild radii above the disk plane, with the mass of the black hole as a free parameter. We searched the parameter space of black hole masses and observer azimuthal angles but we were unable to reproduce a UV light curve which would resemble, even remotely, the observed one. We then explored under what conditions it would be possible to obtain model UV light curves whose autocorrelation function would match those observed. Even though we considered black hole masses as large as 109 M\odot no such matching was possible. Our results indicate that some of the fundamental assumptions of this model will have to be modified to obtain even approximate agreement between the observed and model X-ray -- UV light curves.
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