Compton scattering phase function (left) Phase function for fully polarised photons (P_L = 1), with φ − γ being the azimuthal scattering angle relative to the incoming polarisation direction. The solid and dashed lines correspond to energies of 2 and 8 keV, respectively (right). For unpolarised photons (P_L = 0), the Compton phase function is symmetric around the incoming direction k, while for fully polarised photons (P_L = 1), it is symmetric around the incoming polarisation direction p. For partially polarised photons, the phase function is truly asymmetric.