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 to 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 ; 10 23 and 1:5 ; 10 23 cm À2 separated by approximately 20 yr, 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.

We discuss methods to compute significance levels for the existence of quasi-periodic oscillations (QPOs) in Active Galactic Nuclei (AGN) which take the red-noise character of the X-ray lightcurves of these objects into account. Applying epoch folding and periodogram analysis to the XMM-Newton observation of the Seyfert galaxy Mrk 766, a possible QPO at a timescale of 4200 s has been reported. Our computation of the significance of this QPO, however, shows that the 4200 s peak is not significant at the 95% level. We conclude that the 4200 s feature is an artifact of the red-noise process and not the result of a physical process within the Active Galactic Nuclei.

Abstract. The magnetic Cataclysmic Variable (mCV) V1432 Aql (RX J1940.1-1025) belongs to the four-member subclass of near-synchronous polars with a slight non-synchronism (<2%) between the spin period of the white dwarf and the binary period. In these systems the accretion geometry changes periodically with phase of the beat cycle. We present the application of a dipole accretion model for near-synchronous systems developed by Geckeler & Staubert (1997a) to extended optical and X-ray data. We detect a significant secular change of the white dwarf spin period in V1432 Aql of dP spin /dt = −5.4−9 s/s from the optical data set alone. This corresponds to a synchronization time scale τ sync = 199 +441 −75 yr, comparable to the time scale of 170 yr for V1500 Cyg. The synchronization time scale in V1432 Aql is in excellent agreement with the theoretical prediction from the dominating magnetic torque in near-synchronous systems. We also present period analyses of optical CCD photometry and RXTE X-ray data, which argue against the existence of a 4000 s period and an interpretation of V1432 Aql as an intermediate polar. The dipole accretion model also allows us to constrain the relevant parameters of the accretion geometry in this system: the optical data allow an estimate of the dimensionless parameter (R t0 /R wd ) 1/2 sin β = 3.6 +2.7 −1.1 , with a lower limit for the threading radius of R t0 > 10 R wd (68% confidence).

Abstract.We report on the analysis from ∼110 ks of X-ray observations of Centaurus A carried out with the Proportional Counter Array (PCA) and the High Energy X-ray Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE) during three monitoring campaigns over the last 4 years (10 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 measured 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 detected. We present the interpretation of the iron line strength through Monte Carlo computations of various geometries. No significant temporal variability was found in Cen A at time scales from days to tens of minutes.

The X-ray Multi Mirror Mission (XMM) , the second corner stone mission of the European Space Agency's Horizont 2000, will be launched in December 1999. One of the instruments on board of XMM will be the EPIC pn-CCD. The detector consists of four independent quadrants integrated monolithically on a single silicon wafer. Each quadrant is divided into 3 CCDs with 200 x 64 pixels ( 150 x 150 pm each) and 280 pm depletion depth.The pn-CCD will be able to perform high resolution timing analysis as well as high throughput imaging and spectroscopy in six different readout modes. In the standard imaging mode (Full Frame Mode) the CCDs are read out sequentially every 73.3 ms. In addition, different readout modes allow high resolution timing analysis by reducing the integration time down to 7 s and reading out only one CCD.In this paper we show results of the calibration of the flight spare unit of the EPIC pn camera with respect to time resolution of all observation modes. In the first part we explain the detailed timing of each mode and show how one can calculate the best possible arrival time for photons in each observation mode. In the second part of the paper, we analyzed the influence of the readout noise on the time resolution of the pn-CCD camera, by combining dead time functions with simulated light curves.