RXTE monitoring of Centaurus A

We report on the analysis from similar to 110 ks of X-ray observations of C entaurus A carried out with the Proportional Counter Array (PCA) and the Hi gh Energy X-ray Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE) during three monitoring campaigns over the last 4 years (1 0 ks in 1996, 74 ks in 1998, and 25 ks in 2000). The joint PCA/HEXTE X-ray spectrum can be well described by a heavily absorbed power law with photon index 1.8 and a narrow iron line due to fluorescence of cold matter. The me asured column depth decreased by about 30% between 1996 and 2000, while the detected 2-10 keV continuum flux remained constant between 1996 and 1998, but increased by 60% in 2000. Since in all three observations the iron line flux did not vary, a corresponding decrease in equivalent width was noted. No appreciable evidence for a reflection continuum in the spectrum was det ected. We present the interpretation of the iron line strength through Mont e Carlo computations of various geometries. No significant temporal variabi lity was found in Cen A at time scales from days to tens of minutes.