Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...220..353b&link_type=abstract
Astrophysical Journal, Part 1, vol. 220, Feb. 15, 1978, p. 353-362.
Astronomy and Astrophysics
Astronomy
17
Electron Transitions, Gamma Rays, Ion Sources, Radio Galaxies, X Ray Spectra, Energy Levels, Gamma Ray Astronomy, Ionic Collisions, Ionization Cross Sections, Iron, Nuclear Reactions
Scientific paper
X-ray production at about 6.8 keV by the 2p to 1s transition in fast hydrogen- and helium-like iron ions is calculated, following both electron capture to excited levels and collisional excitation. A refinement of the Oppenheimer-Brinkman-Kramers (1930) approximation is used to obtain an improved charge-exchange cross-section. This, and the corresponding ionization cross section, were used to determine equilibrium charge fractions for iron ions as functions of their energy. The effective X-ray line production cross section was found to be sharply peaked in energy at about 8 to 12 MeV per amu. Since fast ions of similar energies can also excite nuclear levels, the ratio of selected strong gamma-rays line emissivities to the X-ray line emissivity is calculated. These calculations are employed to set limits on the intensity of gamma-rays line emission from the galactic center and the radio galaxy Cen A, and it is found that these limits are generally lower than those reported in the literature.
Bussard Robert W.
Omidvar Kazem
Ramaty Reuven
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