The Hard X-ray Spectrum of the Radio-Galaxy Centaurus A

The radio galaxy Centaurus A has been observed by the BeppoSAX satellite five times from 1997 to 2000. From July 6, 1999 to August 17, 1999 the source was also simultaneously observed with the Comptel instrument onboard of gamma satellite CGRO, allowing the coverage of a very wide energy band (from about 0.4 keV to 30 MeV). BeppoSAX indicates a complex soft spectrum with multiple components and a strongly absorbed (NH about 10<SUP>23</SUP> cm<SUP>-2</SUP>) nuclear hard component (Gamma about 1.8) which becomes steeper at higher energies. BeppoSAX and Comptel data show unequivocally that the nuclear emission has a sharp cutoff at E<SUB>cutoff</SUB> about 600-1000 keV. The continuum of Centaurus A is probably a mixture of beamed and unbeamed components. We do not exclude that the high energy break is the signature of an accretion disk. A complex feature in emission at 6-7 keV is also resolved. We can distinguish at least two components a narrow cold (E=6.4 keV) and an ionized (E=6.8 keV) line. The flux variations do not produce significant modification of the continuum shape (Gamma and E<SUB>cutoff</SUB>). On the contrary, a feature variation is detected on a time scale of about a year. As the strength of the feature is not correlated to the nuclear intensity, we conclude that the primary X-ray source and the reprocessing material are spatially separated.