Preparations

 

A short overview is given about the procedures which one has to carry out to get the right input for the spectral analysis task. Details about this matter can be found in chapter 4 (Data Preparation).

• Creation of a raw spectrum

  Starting from an event file all photons coming from a source in a certain spatial region have to be selected. That means that at least the position of the source has to be known. Then selections of photons belonging to that source can be done according to given conditions by projection commands like SELECT/RING, SELECT/BOX, SELECT TIME, etc. If the photons are properly selected one can bin their pulse height amplitudes   or channels (PHC)   to a raw spectrum with help of the BIN AMPLITUDE command.

• Corrections of a raw spectrum

  There are two places in EXSAS to calibrate raw-data sets for all kinds of efficiencies (like mirror reflectivity, imaging errors, detector efficiency, dead time, filter pass band, etc.).:         The first place is during data preparation using SET/PROJECTION in order to switch on the correction mode. If a raw-spectrum is already created without using the correction mode a correction can still be performed at a second place via the two commands CREATE/PARFIL CORR and CORRECT/SPECTRUM.

  For a complete understanding of applying corrections in order to get an appropriate spectrum it is worth while to study in detail the corresponding sections of chapter 4.

• Preparation of a count rate spectrum

  The binned pulse height amplitudes (raw spectrum) detected from a source and projected out of a photon event file cannot be input directly to the spectral analysis. Such a binned spectrum contains still a background and the counts per bin may be too weak to fulfil the requirements of a fit. The data preparation command PREPARE/SPECTRUM allows

  • to perform a background subtraction by taking into account different time intervals and spatial selections of source and background, which yields in a count rate spectrum .
  • to rebin a count rate spectrum by controlling the statistic of each bin.
• Binning of a detector response matrix     Since the product of the detector response matrix and the correction vector   transforms the vector of the photon flux spectrum , given at m energy points , into a pulse height spectrum   of n channels (folding procedure)  

  

  the matrix must correspond with the n channels of the observed count rate spectrum. In other words, one side of the detector response matrix must match the binning of the observed count rate spectrum. This binning can be performed by command BIN/DETECTOR_RESPONSE, where the binned information is taken from the observed count rate spectrum.