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The absorption of X-rays and gamma-rays in interactions with the cosmic thermal background and baryonic matter at cosmological redshifts is studied. Analytical formulae for the optical depths to photoionization, Compton scattering, photon-matter pair production, photon-photon scattering, and photon-photon single- and double-pair production are derived as functions of redshift and photon energy. The redshift-energy plane is divided into regions of dominance of various absorption processes. In particular, it is found that photon-photon scattering (a process not previously considered in astrophysics) is important for certain ranges of photon energy and redshift.
Zdziarski et al. (1989) studied this question.