Deriving HRC-I Degap for XRCF Settings

Flat Field Data

Flat field illumination of the HRC-I was performed in the HRC lab on 1997 May 22-23 (after the XRCF calibration). The MCP HV and trigger thresholds were set at the levels used during the XRCF calibrations. The data were captured using the flight electronics and a spacecraft interface simulator that would allow data rates ten times greater than in flight. The raw data files contain records consisting only of packed MCP event data.

Raw data fileX-ray lineX-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.

HRC-I Combined
Flat-Field Image (Undegapped)

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.

Projections: HRC-I
Undegapped Flat-Fields at XRCF Settings

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"

Dr. Michael Juda
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Mail Stop 70
Cambridge, MA 02138, USA
Ph.: (617) 495-7062
Fax: (617) 495-7356