Chapter V Cosmic Background X-Rays

概要

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Observations of the diffuse component of cosmic X-rays are reviewed. Theoretical attempts of interpreting its intensity and spectrum in terms of the metagalactic origin of the diffuse X-rays are discussed in the framework of evolutionary cosmology. The presence of the metagalactic diffuse X-rays implies that the intergalactic space is transparent for X-rays. Consequently, helium should be mostly ionized and the abundance of metallic elements should be smaller by a factor of about 10^<-4> than that of hydrogen. Difficulties are pointed out in accounting for the absolute intensity and a break of the energy spectrum at several tens of KeV. The inverse Compton collisions of relativistic electrons with universal microwave photons and with infrared photons in the vicinity of infrared sources give too low values of the break energy. The bremsstrahlung and innerbremsstrahlung induced by cosmic rays in the metagalactic medium may contribute to the diffuse X-rays, if evolutionary effects are taken into account. The result is sensitive to the values of parameters and can hardly explain all features of the diffuse X-rays, in particular their soft component. It is discussed that the cosmic rays are responsible for the heating of the metagalactic medium and consequently play an important role in the thermal history of the universe.
理論物理学刊行会の論文
1972-02-29