[Previous] | [Session 16] | [Next]
G. V. Brown (NASA/GSFC and The Johns Hopkins University), XRS Instrument Team
As part of the ground calibration program for the XRS instrument to be flown on the Astro-E2 X-ray Observatory we have measured the x-ray transmittance of each of the five blocking filters as a function of photon energy. These blocking filters are located at five different thermal stages on the XRS: the calorimeter thermal stage, the front end assembly, the neon shield, the inner vapor cooled shield, and the dewar main shell. Each filter is made by the Luxel Corporation and is comprised of approximately 1000 Åof polyimide and 1000 Åof aluminum. In the case of the dewar main shell filter, the polyimide/aluminum filter is supported by an evenly spaced nickel mesh. We use a grating spectrometer to measure the transmittance in three different spectral orders spanning the region between the oxygen K edge at ~ 540 eV and the aluminum K edge at ~ 1560 eV. We also use a double-crystal monochromator to measure the x-ray transmittance near the nickel K edge at 8333 eV. In flight it is possible, though unlikely, that the overall transmittance of the blocking filters may change as a result of the accumulation of water ice or hydrocarbons outgassing from the spacecraft. An indication of ice is a change in the low energy efficiency caused predominantly by an increase in the areal density of oxygen. After the flight cryostat has been integrated into the neon dewar and prior to launch, we check for water ice by measuring the oxygen absorption edge strength with a continuum x-ray source. During flight, in addition to measuring the oxygen absorption edge itself, we will continue to monitor ice accumulation by measuring changes in relative line intensities that are most sensitive to changes in oxygen accumulation. These measurements will be compared to results gathered on the ground and from other x-ray observatories. An overview of the results from our ground calibration and the observational plan for monitoring the x-ray transmittance of the blocking filters during flight will be presented.
[Previous] | [Session 16] | [Next]
Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.