The parameters, as done in the default parameter file, should be set in order to have:
A well described approach to perform a point-like source analysis can be found in Petry et al. (2009). In their work, the isotropic component is modelled as the product of a common scaling factor and a relative sensitivity for each of the 19 detectors of SPI (taking into account the detector failures during the course of the mission so far). The relative detector sensitivity is permitted to vary on a timescale of 10 revolutions (nearly 30 days) as a compromise between assuming no variability at all (resulting in a degraded fit) and the minimum reasonable variability timescale of one revolution (approx. 3 days, resulting in larger uncertainties due to the increased number of fit parameters). Assuming a shorter timescale than 30 days only change the results within their statistical errors.
The common background scaling factor is permitted to vary on a short timescale of 2h (corresponding to typically four science windows). This is the conservative choice determined by the actually observed changes in the overall event rate (which is strongly dominated by background) and the aim to minimise the number of model parameters in order to improve sensitivity.
A default energy binning can be chosen based on considerations of SPI energy resolution and flux sensitivity. It consists of 20 energy bins of logarithmically increasing width between 25 and 8000keV. with a narrower bin around the 511keV pair annihilation line. Many sources are too weak to be detected significantly above 200keV in individual bins of even this coarse (compared to the SPI energy resolution) energy binning. So a wider binning consisting of 12 bins can be introduced for weaker sources. The narrow and the wide binning should have the first three bins (up to 48keV) in common, then the wider binning roughly combines every two narrow bins up to 500 keV and after that every 3 narrow bins. The bin boundaries of the narrow binning could for instance be 25, 31, 39, 48, 60, 75, 93, 116, 144, 179, 223, 278, 346, 502, 520, 668, 832, 1036, 1290, 1606, 2000, and 8000keV. The bin boundaries of the wider binning could be 25, 31, 39, 48, 70, 103, 150, 219, 320, 502, 520, 1000, and 8000keV.
When the model is constructed, all parameters can be tested for relevance, and parameters which do not show an effect on the fit function can be excluded. Using a maximum likelihood fit which is initialised from a -fit, the model is then fit to the data and the statistical errors are determined from the covariance matrix. For more details see the spimodfit specific handbook. The entire analysis can be carried out independently in each energy bin such that boundary conditions such as variability timescales and the input point source catalog can in principle be chosen differently for each energy bin. This also allows for parallel computation. However, spectra should then be collected by the user with tools which should be developed ad hoc.
If the user should run again spimodfit outside the spimodfit_analysis chain,
since its products are not attached to the observation group, he/she should manually delete the previous results, e.g. with the command:
rm spectr* back_model*spimodfit* res* fitquality.fits
spimodfit_rmfgen.csh lightcurves.fits catalogue.spimodfit.fits