New Constraints on the Continuum Emission Mechanism of Active Galactic Nuclei: Intensive Monitoring of NGC 7469 in the X‐Ray and Ultraviolet

We have undertaken near-continuous monitoring of the Seyfert 1 galaxy NGC7469 in the X-ray with RXTE over a ~30d baseline. The source shows strongvariability with a root-mean-square (rms) amplitude of ~16 per cent, andpeak-to-peak variations of a factor of order 2. Simultaneous data over thisperiod were obtained in the ultraviolet (UV) using IUE, making this the mostintensive X-ray UV/X-ray variability campaign performed for any active galaxy.Comparison of the continuum light curves reveals very similar amplitudes ofvariability, but different variability characteristics, with the X-rays showingmuch more rapid variations. The data are not strongly correlated at zero lag.The largest absolute value of the correlation coefficient occurs for ananticorrelation between the two bands, with the X-ray variations leading the UVby ~4d. The largest positive correlation is for the ultraviolet to lead theX-rays by ~4d. Neither option appears to be compatible with any simpleinterband transfer function. The peak positive correlation at ~4d occursbecause the more prominent peaks in the UV light curve appear to lead those inthe X-rays by this amount. However, the minima of the light curves arenear-simultaneous. These observations provide new constraints on theoreticalmodels of the central regions of active galactic nuclei. Models in which theobserved UV emission is produced solely by re-radiation of absorber X-rays areruled out by our data, as are those in which the X-rays are produced solely byCompton upscattering of the observed UV component by a constant distribution ofparticles.