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: http://xmm.vilspa.esa.es/sas/7.1.0/doc/arfgen/node27.html
Дата изменения: Thu Nov 15 16:15:38 2007 Дата индексирования: Sat Dec 22 08:43:12 2007 Кодировка: Поисковые слова: annular |
In the case of a point source, arfgen can correct for the flux that is outside the region(s) over which the spectrum was accumulated. These regions are read from the spectrum's DSS information. The correction works by taking a model of the PSF from the CAL, centred at the source position and calculating the total fraction of that PSF within the regions of interest.
To enable the encircled energy correction for point sources, the parameter extendedsource must be set to false, as well as modelee being set to true.
The encircled energy correction is energy dependent, so ideally the EE should be computed for each and every point on the energy grid. However, given that the EE calculation is computationally intensive, the option to resample the energy grid is provided by the parameter eegridfactor. The resultant EE correction vector is interpolated back onto the original energy grid, and each ARF element is corrected using the corresponding EE correction factor. See section 12 for further information.
The encircled energy or PSF which arfgen extracts from the CCF and uses is dependent on the shape of the source region. For the common case of a circular, rectangular or annular region centred on the source, a formulation of the enclosed energy as a function of energy, off-axis angle and box radius is used (EXTENDED mode). This is the most accurate representation available at the moment. For other source box shapes an energy independent map is used which is only strictly valid for energies below 4.5 keV. A region consisting of an included and an excluded circle is considered to be an annulus in this context if the centre of the two shapes is the same within 1 arcsecond.