Simulated high-energy spectrum from the corona in Cygnus X-3 with BELM. The multicolor black-body spectrum from the accretion disk (black dotted line) is comptonized by a population of thermal and non-thermal electrons that are heated and accelerated in the corona up to a maximum Lorentz factor γ_max = 2 × 10⁵. The black line shows the best-fit solution (not corrected from absorption of soft X-rays by the ISM and the stellar wind) to the X-ray data (archive RXTE data, pink crosses from Szostek et al. 2008) in the ultra-soft state given in Hjalmarsdotter et al. (2009). This solution corresponds to a corona of radius R_c = 8 × 10⁷ cm and a total unabsorbed bolometric luminosity L_bol = 3.6 × 10³⁸ (at 9 kpc). This figure also shows the spectra for R_c = 8 × 10⁸ (green), 8 × 10⁹ (blue) and 8 × 10¹⁰ cm (red), assuming the same bolometric luminosity. The dashed lines are the intrinsic spectra (without pair production) and the solid lines are the absorbed spectra that reach the observer. The Fermi power-law taken from Abdo et al. (2009) is overplotted for comparison.