INTEGRAL and RXTE Observations of Centaurus A

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 x 10{sup 23} cm{sup -2} and 1.5 x 10{sup 23} cm{sup -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

Law and state:A Biannual Collection of recent German Contributionsto these Fields

133 hal.;25 c

Generic Completion (Version 1)

Abstract rewrite systems define a reduction relation by a set of rules. An important aspect of such rewrite relations is their behavior in an arbitrary context associated with the underlying congruence relation. This behavior is described by "compatibility properties": a rewrite system is compatible if applying the same context to two objects preserves the rewrite relation among them. We present a generic completion procedure for abstract rewrite systems and characterize the minimal compatibility requirement for rewrite relations that are necessary to describe completion procedures as proof transformation procedures. This requirement (called sufficient compatibility) subsumes the class of semi-compatible rewrite relations that play an important role in algebraic completion. In order to allow for non-compatible rewrite relations we must replace the concept of equations (critical pairs) by promises which leads to a new proof transformation relation and a new proof ordering for abstract r..