THE AVERAGE X-RAY GAMMA-RAY SPECTRUM OF RADIO-QUIET SEYFERT 1S/

We have obtained the average 1-500 keV spectrum of radio-quiet Seyfert Is using data from EXOSAT, Ginga, HEAO-1 and GRO OSSE. The spectral f it to the combined average EXOSAT and OSSE data is fully consistent wi th that for Ginga and OSSE, confirming results from an earlier Ginga/O SSE sample. The average spectrum is well fitted by a power-law X-ray c ontinuum with an energy spectral index of alpha similar or equal to 0. 9 moderately absorbed by an ionized medium and with a Compton reflecti on component. A high-energy cut-off (or a break) in the power-law comp onent at a few hundred keV or more is required by the data. We also sh ow that the corresponding average spectrum from HEAO-1 A1 and A4 is fu lly compatible with that obtained from EXOSAT, Ginga and OSSE. These r esults confirm that the apparent discrepancy between the results of Gi nga (with alpha similar or equal to 0.9) and the previous results of E XOSAT and HEAO-1 (with alpha similar or equal to 0.7) is indeed due to ionized absorption and Compton reflection first taken into account fo r Ginga but not for the previous missions. Also, our results confirm t hat the Seyfert 1 spectra are on average cut off in gamma-rays at ener gies of at least a few hundred keV, not at similar to 40 keV (as sugge sted earlier by OSSE data alone). The average spectrum is compatible e ither with emission from an optically thin relativistic thermal plasma in a disc corona, or with a non-thermal plasma with a power-law injec tion of relativistic electrons.