Point sources

1. Create an image of the whole field using XSORT

        ICL> XSORT  SRCFILE=CYGX1_IMAGE
        

2. Display the image using the 'I' routines.

        ICL> ILOAD  CYGX1_IMAGE
        ICL> IDISPLAY
        

3. Choose source and background box centres and sizes

        ICL> XRTBCKBOX
        

   This will allow you to use a cursor on the image to select the position and radius of a source and background box. It then sorts events from within these boxes into a source and background spectrum.
4. Background subtract the source file

        ICL> XRTSUB
        

   This corrects the background spectrum to that which would have been seen had this background been at the position of the source box. It then subtracts it from the source spectrum.

   NB: the correction of the background spectrum to the source position is a vignetting correction which is performed on a pulse height channel basis. In reality vignetting corrections are only calibrated for photon energies. So a small third order error is introduced by assuming that we know the "energy" of each corrected pulse height bin.

5. Correct the subtracted spectrum

        ICL> XRTCORR
        

   This will correct the spectrum for the energy independent effects, dead time and wires. In addition it produces an array of energy dependent correction factors within the datafile. These are used as the effective area at each energy for this datafile.

6. Produce a detector response matrix

        ICL> XRTRESP
        

   This multiplies the detector matrix file with the energy corrections array found in the corrected datafile. The resultant energy response structure is stored in the datafile.

7. Set up a spectral model and fit the data

        ICL> SMODEL
        ICL> SFIT