INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Centaurus 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 .
Cen A was detected by both sets of instruments from 3–240 keV .
When combined with earlier archival RXTE results , we find the power law continuum flux and the line-of-sight column depth varied independently by 60 % between 2000 January and 2003 March .
Including the three archival RXTE observations , the iron line flux was essentially unchanging , and from this we conclude that the iron line emitting material is distant from the site of the continuum emission , and that the origin of the iron line flux is still an open question .
Taking X-ray spectral measurements from satellite missions since 1970 into account , we discover a variability in the column depth between 1.0 \times 10 ^ { 23 } cm ^ { -2 } and 1.5 \times 10 ^ { 23 } cm ^ { -2 } separated by approximately 20 years , and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause .
The INTEGRAL OSA 4.2 calibration of JEM-X , ISGRI , and SPI yields power law indices consistent with the RXTE PCA and HEXTE values , but the indices derived from ISGRI alone are about 0.2 greater .
Significant systematics are the limiting factor for INTEGRAL spectral parameter determination .