BeppoSAX observations of the radio galaxy centaurus A Original Research Article

We present preliminary results from two observations of the radio galaxy Centaurus A performed by the BeppoSAX satellite on 1997 February 20–21 and on 1998 January 6–7. In the second pointing the source was brighter by a factor 1.3. We did not detect any spectral variation of the nuclear continuum in spite of the long-term flux change between the two observations. At both epochs, the nuclear point-like emission was well fitted with a strongly absorbed (NH ∼ 1023cm−2) power law with an exponential cutoff at high energies (Ecut > 200keV). We also observed a significant flux variation of the iron line between the two observations. The flux of the line and of the continuum changed in the opposite sense. The line is more intense at the first epoch, when the nuclear source was at the lower intensity level. The implied delay between the continuum and line variations strongly suggests that the cold material responsible for the iron line production is not located very near to the primary X-ray source. There is also evidence that the line profile changed between the two epochs, being broader and slightly blueshifted when the source was fainter. It is possible that the emission feature is a blend of cold and ionized iron lines produced in separate regions surrounding the nuclear source.