Magnetic two-photon scattering and two-photon emission: Cross sections and redistribution functions

We discuss the magnetic two-photon scattering cross section within the framework of quantum electrodynamics, and calculate explicitly the corresponding scattering redistribution function for this process and its inverse, as well as the scattering source function. We calculate in a similar way the magnetic two-photon emission process which follows the radiative excitation of Landau levels above ground. The two-photon scattering and two-photon emission are of the same order as the single-photon magnetic scattering. All three of these processes, and in optically thick cases also their inverses, are included in radiative transport calculations modeling accreting pulsars and gamma-ray bursters. These processes play a prominent role in determining the relative strength of the first two cyclotron harmonics, and their effects extend also to the higher harmonics.