HEXE OBSERVATIONS OF ACTIVE GALACTIC NUCLEI - CONSTRAINTS ON PAIRS AND COMPTON REFLECTION

We present results of X-ray observations of the three brightest Active Galaxies in hard X-rays, the quasar 3C 273 (1226+02), the Seyfert galaxy NGC 4151, and the radio galaxy Cen A (NGC 5128). The observations were made with the HEXE instrument (20-200 keV) on board the Mir space station. We discuss the spectra of the sources in the context of models including pair production, reflection and spatially separated emission regions. We find that pairs play a minor role in 3C 273 and Cen A. The relative contribution of a reflected component cannot be constrained from our data, but the "canonical" model with simple pair cascades and Compton reflection can be ruled out for 3C 273 and Cen A. For NGC 4151, the importance of reflection can be constrained by the combined analysis of data from HEXE and Ginga taken simultaneously.