When estimating source flux and spectral evolution from 1s ratemeters data or fitting the 240 channels spectra, we have also to account for systematic effects
due to the uncertainties in the description of detectors efficiencies.
As we have discussed in chapter 3, the dependency of LS1 and LS3 efficiencies
have been obtained by fitting the calibration data with an analytical function.
Thus, the error on the estimated efficiency for a given energy and direction is
calculated by propagating the errors on the function parameters, which in turn are determined by the errors on the calibrations data. The errors on the calibrations data are obtained by propagating in the background subtraction the Poissonian variance and by accounting of the uncertainty in the calibration source flux,
which is taken to be 10%.
In this way it is possible to estimate the uncertainty in detectors efficiency for each ratemeters band and PHA channel for the source position. The uncertainty in finally quadratically added to the data statistical variance.