Physical Interpretation of the UV/X-Ray Variability Behavior of NGC 7469

We present a re-analysis of the simultaneous 30 day IUE/XTE observation ofNGC 7469 done in 1996. Our main progress, in comparison to previous spectralanalysis, is to adopt and fit directly to the data a detailed Comptonizationmodel. This firstly allows to fit simultaneously the data from the UV to thehard X-ray band in a self-consistent way and secondly it gives directconstraints on the physical parameters of the disc-corona system. Our resultsare completely consistent with a slab geometry where all the observed UVemission is supposed to cross the corona but more photon-starved geometriesalso give acceptable fits. Whatever the geometry is, the UV seed photonemission appears to be dominated by the reprocessing of the X-rays. We alsofound very interesting correlations between the different model parameters, themost important one being the anticorrelation between the corona temperature andthe UV flux. Such an anticorrelation is clearly inconsistent with a fixeddisc-corona configuration and suggests a variation of the geometry of thesystem. We also find a correlation between the corona optical depth and theX-ray flux which may reflect processes linked to the corona formation. Duringthe observations, NGC 7469 appears to accrete near its Eddington limit. Thissource could then be an example of magnetically dominated disc-corona system asrecently proposed by Merloni (2003).Comment: 12 pages, 6 figures accepted in Astronomy & Astrophysic