The effect of X-ray absorption fine structure in soft X-ray astronomical telescopes

Journal Article · Sat Feb 01 04:00:00 EST 1997 · Astrophysical Journal

DOI:https://doi.org/10.1086/303628· OSTI ID:530002

Owens, A; Denby, M; Wells, A; Keay, A ^[1]; Graessle, D E ^[2]; Blake, R L ^[3]

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1. Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH (United Kingdom)
2. Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge , Massachusetts 02138 (United States)
3. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

Recent in-orbit measurements by high resolution soft X-ray telescopes have revealed low-level fine structure in target spectra that cannot be attributed to a celestial source. Ultimately, this can be traced to the ability of the new high spectral resolution silicon detectors to resolve X-ray absorption fine structure (XAFS) produced in the various detection subsystems. Based on measurements taken at the Daresbury Synchrotron Radiation Source (SRS) and the National Synchrotron Light Source (NSLS), we have modeled the full-up response function of the Joint European X-ray Telescope (JET-X), taking into account edge structure generated in the detectors, filters, and mirrors. It is found that unfolding celestial source spectra using a response function in which the detailed edge shapes are calculated from standard absorption cross sections leads to the generation of spectral artifacts at every absorption edge. These in turn produce unacceptably high values of {chi}{sup 2} in model fits for total source fluxes above {approximately}4{times}10{sup 4} counts. For JET-X, this corresponds to a source strength of {approximately}0.4millicrab observed for 10{sup 5}s. Statistically significant {open_quotes}linelike{close_quotes} features are introduced into the derived source spectra with amplitudes as great as 10{percent} of the source flux. For JET-X, these features rise above the 3 {sigma} level for integral source exposures above {approximately}5{times}10{sup 4} source counts. The largest deviations in the residuals arise near 0.5 keV and 2.2 keV and are attributed to XAFS produced in the oxide surface layers of the CCD and the gold reflective surface of the mirrors, respectively. These results are significant for data interpretation tasks with the {ital ASCA}, JET-X, {ital XMM}, and {ital Advanced X-Ray Astrophysics Facility} ({ital AXAF}) telescopes. {copyright} {ital 1997} {ital The American Astronomical Society}

• OSTI ID: 530002
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 476; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

44 INSTRUMENTATION
INCLUDING NUCLEAR AND PARTICLE DETECTORS
ENERGY LOSSES
FINE STRUCTURE
QUANTUM EFFICIENCY
RESOLUTION
TELESCOPES
X-RAY EQUIPMENT