High-energy spectral changes in three Seyfert galaxies observed with GINGA.

The authors have analysed observations of the three Seyfert Galaxies IC 4329A, MCG -6-30-15 and NGC 4051 extracted from the GINGA archive. The variations in the (4 - 18)keV spectrum of the three sources can be interpreted in the framework of a model with two components: a "direct" power law with constant spectral index (α = 1.9 - 2.1), and the "reflection bump" predicted by Guilbert and Rees, and Lightman and White which is produced by reprocessing of the direct power law in optically thick matter in the surroundings of the central source. The differences found in the behaviour of the three sources would arise, in this scenario, from the different size of the "reprocessing region".