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Setting up the data and finding the MLE
A minimal setup script. The fakeit step builds the simulated spectrum; in practice you would substitute a real spectrum here.
statistic cstat
abund angr
xsect vern
xset delta 0.01
model TBabs*apec & 0.05 & 1.0 & 1.0 & 0.0 -1 & 0.04 &
fakeit none & aciss_aimpt_cy16.rmf & aciss_aimpt_cy16.arf
& y & & fake.fak & 10000.0 & 1.0 & 10000.0 &
data 1:1 fake.fak
ignore **-0.5 8.0-**
method leven 1000 0.005
fit
fit
The two consecutive fit calls let XSPEC refresh the covariance matrix after any parameter that was temporarily frozen during the first pass thaws back – the second fit converges in zero iterations and updates the Hessian, which the samplers below will use as their warm-start proposal.