Upper panel: comparison of two phase-averaged synthetic spectra in terms of counts detected by NICER with T = 2.0 MK, and one week exposure time of object similar to PSR J0437−4715. The other parameters of the model are the same as explained in Sect. 2 (e.g. the spot size remains 5.0°). The blue bars are calculated with the Thomson model MCPHAC and the red bars are for our full Compton model. Every twenty adjacent NICER energy bins are combined to one bin. A calibration error of 1% is assumed. Lower panel: relative difference of the counts predicted by the two models. The error bars correspond to the combined error of the two data points in a given energy bin relative to the observed counts of Thomson model, calculated by .