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Calibration of X-ray CCDs with an Erect-Field Grating Spectrometer in the 0.2 - 1.5 keV band.

G. Prigozhin, M. Bautz, K. Gendreau, G. Ricker
Massachusetts Institute of Technology
Center for Space Research
70 Vassar Str., MA 02139

Goddard Space Flight Center
Greenbelt, MD 20771


X-ray CCDs developed at MIT Lincoln Laboratories for the AXAF CCD Imaging Spectrometer (ACIS) have been calibrated in the 0.25-1.5 keV spectral range using an erect-field grating spectrometer and an electron impact X-ray source in our laboratory. The high resolving power of the spectrometer ( R = 500--1000) coupled with the intrinsic energy resolution of the CCD, allows efficient measurement of the CCD energy scale and spectral response function as essentially continuous functions of energy over the spectrometer passband. The CCD energy scale is found to be linear to approximately 0.5% in this spectral band. Relative variations in the detection efficency of the CCD can also be studied with this system. A near edge structure is detected in the CCD response around the Oxygen K absorption edge. Both frontside and backside illuminated devices have been examined, and, as expected, near edge structure is found to be much stronger for the frontside illuminated CCD. Comparison of these results with the data acquired with a synchrotron radiation source and monochromator confirms that these structures are features of the detector response. The edge structure allows us to measure the absolute dispersion relation of the spectrometer (and hence the zero-point of the CCD energy scale) with a precision better than 1 eV. We also detect considerable structure in characteristic nitrogen and oxygen emission lines from the electron impact source. We discuss likely mechanisms for the production of this structure.

Keywords: X-rays, charge coupled devices (CCD), X-ray spectrometers, X-ray absorption fine structure (XAFS)