The X-ray structure of Centaurus A from 0.1 to 50 keV observations with Exosat

The results from four Exosat observations of the radio galaxy Centaurus A performed during 1984-1985 are presented. The emission from the nucleus detected in the medium-energy X-ray band exhibits time variability on all time scales from a few minutes to years. Small changes are detected in the spectra of the source obtained at the different epochs. All spectra are well fitted by a power law with energy index alpha = 0.70 and strong low-energy photoelectric absorption, with an absorbing column N(H) variable between 1.4 and 1.7 x 10 to the 23rd/sq cm. An unabsorbed component is observed at low energies in all spectra which can be fitted with a thermal spectrum with T roughly 1.6 keV and which is consistent with the integrated emission of the spatially extended sources outside the nucleus. An iron fluorescence line is detected at 6.4 keV which seems to be constant in absolute intensity. The iron K-absorption edge at 7.1 keV is also observed, and the abundance of absorbing iron relative to lighter elements is larger than the cosmic value. 43 refs