Comparison of the confidence regions on the mass-radius plane for the CCO in HESS J1731−347 using the spectra of the pure carbon atmosphere models computed with (solid black contours) and without (dashed green contours) Compton scattering. The contours correspond to 50, 68, and 90% confidence levels for the two parameters of interest. The assumed distance to the source is 3.2 kpc. The reduced (895 d.o.f.). The thin gray curves indicate the mass-radius dependencies for some of the commonly used nuclear EoS.