Constraints on the High Energy Continuum of Seyfert galaxies from RXTE Color-Color and Color-Flux Diagrams

We report on some results from a three-year program of RXTE observations of 4 Seyfert galaxies: NGC 4051, NGC 5548, MCG-6-30-15 and NGC 5506. We focus here on color-color and color-flux diagrams obtained using the count-rates of the PCA instrument in different energy ranges: 3--5, 5--7 and 7--10 keV. The data of the different sources show interesting trends in the different color-color and color-flux planes. These trends are quite similar from one source to the other, even in the case of the narrow line Seyfert 1 NGC 4051 which exhibits strong flux and spectral variability. We discuss these results in term of a simple spectral model: a power law with high energy cut-off + reflection + Iron line, with the scope of understanding the relations between the observed variations of different components and the physical causes of the variability.