How to use XSPEC gain command
Users can investigate the effects of the energy scale offset on their data by using the gain fit command in xspec. Since this command works by shifting the energy boundaries of the response matrix, rather than by changing the matrix elements themselves, it should be regarded as an approximation. However, it does provide a simple first step toward addressing the problem. Here's how to proceed:
- Fit the spectrum using the nominal gain.
- If applicable, fix the energies of line features at their expected
values. For example, fix the energy of the fluorescent line from neutral
iron at 6.4 keV.
- At the xspec prompt type gain fit, after which you'll be
prompted for the initial values of the slope and the offset.
- Enter 1,-1 for the slope (to make it a fixed parameter) and hit return for the offset (to make it a free parameter).
-
Next use the fit command to refit the data and derive the model
parameters along with the best-fitting offset which will be listed as the last parameter. It should come out to be a few tens of eV.
If you have any questions concerning ASCA, visit our Feedback form.