X-ray scattering by intergalactic dust

The imaging capabilities of the Exosat and Einstein satellites at soft X-ray wavelengths have begun to show that suitable Galactic X-ray sources have extended ( 10 arcmin) haloes due to scattering of soft X-rays by interstellar dust. A simple argument suggests that similar haloes, due to scattering by intergalactic dust, should exist around distant (z 1) quasars and detailed analysis confirms this conclusion. A search for such haloes around suitable X-ray quasars could provide valuable, model-independent, constraints on the amount and origin of intergalactic dust.     

Global Gravity Field Recovery Using Solely GPS Tracking and Accelerometer Data from Champ

A new long-wavelength global gravity field model, called EIGEN-1, has been derived in a joint German-French effort from orbit perturbations of the CHAMP satellite, exploiting CHAMP-GPS satellite-to-satellite tracking and on-board accelerometer data over a three months time span. For the first time it becomes possible to recover the gravity field from one satellite only. Thanks to CHAMP'S tailored orbit characteristics and dedicated instrumentation, providing continuous tracking and on-orbit measurements of non-gravitational satellite accelerations, the three months CHAMP-only solution provides the geoid and gravity with an accuracy of 20 cm and 1 mgal, respectively, at a half wavelength resolution of 550 km, which is already an improvement by a factor of two compared to any pre-CHAMP satellite-only gravity field model. This revised version was published online in August 2006 with corrections to the Cover Date.     

IVI comes of age: An overview of IVI specifications with current status

IVI stands for Interchangeable Virtual Instruments; the IVI Foundation was formed in 1997 and is a consortium founded to promote standard specifications for programmable test instruments. The foundation focuses on the needs of users who build high performance test systems. By building on existing industry standards, such as VXIplug&play driver concepts, the Foundation's goal is to deliver specifications that simplify interchangeability, provide better performance, and maintainable test programs. To date, only a few IVI drivers have been available. In the past year, the IVI Foundation finished a major revision of it's architecture and has released a blizzard of specifications, increasing its IVI Class specification by 80% and dramatically improving the consistency and quality of released drivers. The DoD has expressed major interest in IVI's success. With the recent successful completion of the current set of specifications, DoD is interested in becoming involved in defining the next set of Class Specifications. The NxTest Working Group lists IVI as a key technical element, and DoD has recently requested that the IVI Foundation consider Electro Optical equipment for their next set of Class Specifications; a Working Group has been formed to more clearly define this activity.     

The X-ray halo of Cygnus X-1

Four EINSTEIN HRI images of Cygnus X-1 were examined for the presence of a halo due to scattering of X-rays by interstellar grains. The analysis technique exploits the intrinsic aperiodic variability of the source to map the point response function of the optics. A residual, non-variable, component to the surface brightness distribution (comprising 12% of the source flux) is interpreted as a scattered halo. The halo flux does not reflect the short term time variability of the central source as it is smoothed by differential time delays of order days. The Cygnus X-1 halo is consistent with those of other sources derived in previous studies using different techniques. Comparison is made with a scattering model, and the sensitivity of the halo flux to maximal grain size is demonstrated.