Come analyze HEASARC, IRSA, and MAST data in the cloud! The Fornax Initiative is now welcoming all interested beta users.
Next: suzpsf: Suzaku surface brightness Up: Mixing Model Components Previous: Failure modes and regularization Contents
recorn: change correction norm for a spectrum
This model is a replacement for and improvement on the old xspec command recornrm. If a correction file is in use for a spectrum then its normalization can be fitted for using this model. The first parameter, which is not variable, is the spectrum number and the second the correction file normalization. The starting value of the second parameter should be set to the current value of the correction file norm (this can be independently set using the cornorm command).
Because recorn rescales the correction file rather than the model flux, the statistic depends on cornorm through the data, and the chain rule used to compute parameter derivatives would evaluate that dependence as zero. XSPEC therefore switches automatically to the slower full numerical differentiation algorithm whenever a free recorn parameter is present, and only for that fit. Earlier versions did not, and required
XSPEC>xset usechainrule noto be given by hand; that is no longer necessary.
Unlike the other mixing models, which perform a single transformation spanning every data group, recorn is applied separately within each data group, because its first parameter names one spectrum. Each data group's copy of the component therefore has its own spectrum number and its own cornorm, and all of them appear in show par. To fit the correction norms of two spectra, put them in separate data groups and untie the second group's copy:
XSPEC>data 1:1 spec1 2:2 spec2 XSPEC>model recorn*phabs*powerlaw XSPEC>untie 6-7 XSPEC>newpar 6 2after which data group 1's copy corrects spectrum 1 and data group 2's corrects spectrum 2. Note the newpar: if the spectrum numbers are left tied, every copy corrects the same spectrum and only the last one applied has any effect.
| par1 | specnum: spectrum number |
| par2 | cornorm: correction file normalization |