## Complete sigma _{perp } = {sigma }^{C}_{perp }+{sigma }^{{ m TR}}_{perp } double differential scattering cross section of a linearly polarized (perpendicular to the plane of scattering, ⊥) x-ray photon by the Mn atom (theory of this paper): solid (dashed) curve—counted (not counted) autoionization channel equation (7)

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**Figure 3.** Complete \sigma _{\perp } = {\sigma }^{C}_{\perp }+{\sigma }^{{\rm TR}}_{\perp } double differential scattering cross section of a linearly polarized (perpendicular to the plane of scattering, ⊥) x-ray photon by the Mn atom (theory of this paper): solid (dashed) curve—counted (not counted) autoionization channel equation (7). Dotted curve—the result of the impulse approximation (from tabulated data [15] for the Compton profiles J_{n_{1}l_{1}}(\chi ) equation (22)). ω_{1} = 5 keV (a), 8 keV (b), θ = 90°, Γ_{beam} = 10 eV, \max ({\sigma }^{{\rm TR}}_{\perp }) = 21.07 r^{2}_{0} \; {{\rm eV}}^{-1} \, {\rm {sr}}^{-1} (a), 12.70 r^{2}_{0} \; {{\rm eV}}^{-1} \, {\rm {sr}}^{-1} (b).

**Abstract**

The existence of the giant autoionization resonance in a double differential cross section of the nonresonant Compton scattering of hard x-ray photons by an atom with an open shell in the ground state is theoretically predicted on the example of the Mn atom. The developed mathematical formalism is based on the multiconfiguration generalization of the nonrelativistic quantum theory of contact inelastic scattering of a photon by an atom, constructed in the work by Hopersky and Nadolinsky (2012 *J. Exp. Theor. Phys.* **115** 402).