Fluorescent lines from the nucleus of Centaurus A

The results of a Centaurus A (NGC 5128) observation with the X-ray satellite ASCA on 1993 August 14 are reported. We have resolved the X-ray emission of this source into those from the nucleus and extended components. The spectrum of the nucleus in the 0.5-10 keV energy range was analyzed. In the energy range above 3 keV, the spectrum of the nucleus can be represented by a heavily absorbed power-law with N-H similar or equal to 10(23) cm(-2) and a Fe K alpha line. The flux of the Fe line implies that it originates from reprocession in the dense matter (N-H similar or equal to 10(23) cm(-2)) which completely surrounds the central X-ray source. In the energy range below 3 keV, the spectrum shows an excess over the power-law spectrum extrapolated from the higher energy range above 3 keV. In the soft excess component, three emission lines have been identified. The center energies of these lines correspond to those of the K alpha lines of neutral Mg, Si, and S. The equivalent widths of these lines and the soft excess can be explained by fluorescence and scattering in relatively cold and thin (N-H similar or equal to 10(22) cm(-2)) matter illuminated by the central X-ray source. The complex configuration of the matter surrounding the central X-ray source is required to explain the flux of the Fe line and the soft excess component at the same time.