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 fit to the combined average EXOSAT and OSSE data is fully consistent with that for Ginga and OSSE, confirming results from an earlier Ginga/OSSE sample. The average spectrum is well fitted by a power-law X-ray continuum with an energy spectral index of alpha similar or equal to 0.9 moderately absorbed by an ionized medium and with a Compton reflection component. A high-energy cut-off (or a break) in the power-law component at a few hundred keV or more is required by the data. We also show that the corresponding average spectrum from HEAO-1 A1 and A4 is fully compatible with that obtained from EXOSAT, Ginga and OSSE. These results confirm that the apparent discrepancy between the results of Ginga (with alpha similar or equal to 0.9) and the previous results of EXOSAT and HEAO-1 (with alpha similar or equal to 0.7) is indeed due to ionized absorption and Compton reflection first taken into account for Ginga but not for the previous missions. Also, our results confirm that the Seyfert 1 spectra are on average cut off in gamma-rays at energies of at least a few hundred keV, not at similar to 40 keV (as suggested earlier by OSSE data alone). The average spectrum is compatible either with emission from an optically thin relativistic thermal plasma in a disc corona, or with a non-thermal plasma with a power-law injection of relativistic electrons.