INTEGRAL and RXTE Observations of Centaurus A
  INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Cen A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the X-ray/low energy gamma ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. When combined with earlier archival RXTE results, we find the power law continuum flux and the line-of-sight column depth varied independently, and the iron line flux was essentially unchanging. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a variability in the column depth between 1.0x10^23 cm^-2 and 1.5x10^23 cm^-2, and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause. 
Richard E. Rothschild, Joern Wilms, John Tomsick, Ruediger Staubert,   Sara Benlloch, Werner Collmar, Grzegorz Madejski, San...