The procedure takes a stack of Fe55 Xray images and analyses the single pixel events to calculate gain and CTE. The input images can be a multiple selection of single images, or a single fits file containing 3D image cube or multiple extensions.
The procedure is called as follows:
The four optional parameters define the window within the image that should be used for the analysis. If omitted, the program will calculate its own window ; one that avoids the edges of the image where there may be bad pixels. Input images are selected using a dialogue. Once read in a histogram of all pixels is displayed and the user is asked to point and click on the peak of the Fe55 spectral line. This should be visible as the larger of a distinct line doublet. An example is shown here. Once the Fe55 line is identified it is then rescaled and the user asked to identify the line a second time using a higher resolution plot of the histogram. The pixels that contain Xray events of the selected energy (+/- 5%) are then filtered from the image and their values plotted in two graphs, the first as a function of column number, the second as a function of row number. Linear fits are made to the pixel values and used to calculate the Horizontal and Vertical CTE respectively. As a double check that the user has selected the correct line, the plots are overlaid with dashed line indicating the predicted positions of two other Fe55 spectral lines. If these dashed lines so not coincide with a spectral line (i.e. a concentration of pixels at a particular energy) then the primary Fe55 line has probably been misidentified.
The program outputs system gain in e/ADU , based on the fact that an Fe55 Xray will produce a charge packet of 1620e- in Silicon. The CTE output is expressed as charge transfer efficiency per transfer.