|Raw data file||X-ray line||X-ray energy|
For deriving degap coefficients all four sets can be combined to improve the statistics. Below is an image of the summed flat field data using undegapped coordinates.
In this image the HRC-I, the V-axis increases from left to right and the U-axis increases from bottom to top. It is obvious from this image that the illumination was not flat. The HRC-I detector was not aligned with the center of the beam in the x-ray pipe, resulting in occultation of the low-V-coordinate corners of the detector. There is also be evidence for a non-uniform response in the detector which will also impact the "flatness" of the flat-field data. The following figure contains histograms of the axis projections of the undegapped data.
The shadowing of the corners of the detector causes a significant gradient in the histograms. These gradients create problems in the derivation of quadratic degapping coefficients; they have less impact on linear coefficients. Discussions of the linear and quadratic coefficients are at the following links.
Back to "HRC Degapping Corrections"
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Mail Stop 70
Cambridge, MA 02138, USA
Ph.: (617) 495-7062
Fax: (617) 495-7356