CONSTRAINING THE COMPLEXITIES IN SEYFERT X-RAY-SPECTRA - AN ANALYSIS OF SIMULTANEOUS OBSERVATIONS WITH GINGA AND ROSAT

Absorption and reprocessing of X-ray photons in the nuclei of active g alaxies have recently been found to alter significantly the appearance of the emergent spectrum. The limited bandwidth and resolution of mos t contemporary X-ray spectral data often leave open differing interpre tations of the nature and magnitude of these effects and, consequently , the precise form of the underlying continuum spectrum. A unique oppo rtunity to examine, over some two decades in energy, the X-ray spectra of five bright Seyfert galaxies. based on simultaneous observations w ith the Ginga and ROSAT satellites, has now provided data to clarify t he form of this reprocessing. In every case, the underlying continuum has a power-law form, with a preferred photon index consistent with th e revised canonical value of 1.9 +/- 0.1. A somewhat surprising result , however, is the range and variety of spectral features superimposed on this continuum. For NGC 4051, the dominant feature is absorption fr om a substantial column density of ionized gas in the line of sight to the continuum source. Division of these data into low- and high-flux states confirms spectral variability for NGC4051, with an indication o f a flux-linked change in the ionization parameter and the emergence, in the hi h state, of a significant soft emission feature. Mrk 841 and 509 both exhibit features attributable to reflection from cold matter , plus a soft excess. In addition, Mrk 509 has a spectral feature near approximately 1 keV that is possibly due to Fe L emission. Finally, f or NGC 7213 and Fairall-9, which both show Fe K emission at an unusual ly high (rest) energy and a soft excess, a good overall spectral fit i s obtained with an ionized-disc model.