Upper panel: angular distribution of the specific intensity as a function of the cosine of the zenith angle μ for the NS atmosphere parameters given in Fig. 1. The outputs of our code (using the Thomson approximation) and those of the MCPHAC code are marked by solid- and dashed-lines, respectively. The black, blue, green, orange, and red colors correspond to 0.1, 0.5, 1.0, 5.0, and 10.0 keV, respectively. Lower panel: relative difference between the normalised angular distributions is shown.