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specgroup (specgroup-1.7.1) [xmmsas_20211130_0941-20.0.0]

Minimum resolution

If the number of counts in a spectrum is very high then a statistical grouping can dramatically oversample the instrument resolution. This can cause problems during spectral fitting because the bins are then not completely independent.

A minimum energy width of each group can be enforced by setting the parameter oversample. e.g.

specgroup spectrumset=srcspec.ds mincounts=25 oversample=3 rmfset=myrmf.ds

would ensure that no group was narrower than 1/3 of the full width half maximum (FWHM) resolution at the central photon energy of the group.

$\Delta E >= FWHM(E)$

where the values of FWHM(E) are read for a given instrument from a calibration file (XMM_SPECQUAL_nnnn.CCF for XMM instruments).

XMM-Newton SOC -- 2021-11-30