To extract a spectrum with the spi_science_analysis script, follow the instructions provided in Sect. . The spi_science_analysis script sets all relevant parameters in the resulting spectra, creates an appropriate response file, and links it to the spectrum.
Below is a simple example of an XSPEC spectral fitting session with a Crab spectrum (spectrum_Crab.fits).
xspec cpd /xs data spectrum_Crab.fits setpl energy model power 2.0 8.0 fit 1000 flux 20,200 plot ldata delchi