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)