Diffuse Γ-ray Research Articles

Gamma Rays from Cosmic Rays

It is shown that there is evidence favouring molecular clouds being sources of γ-rays, the fluxes being consistent with expectation for ambient cosmic rays interacting with the gas in the clouds for the clouds considered. An estimate is made of the fraction of the apparently diffuse γ-ray flux which comes from cosmic ray interactions in the I.S.M. as distinct from unresolved discrete sources. Finally, an examination is made of the possibility of gradients of cosmic ray intensity in the Galaxy.

Cosmic neutrinos of ultra-high energies and detection possibility

The fluxes and spectra of galactic and extragalactic neutrinos at energy 1011–1019 eV are calculated. In particular, the neutrino flux from the normal galaxies is calculated taking into account the spectral index distribution. The only assumption that seriously affects the calculated neutrino flux atE v ≳1017 eV is the power-like generation spectrum of protons in the entire considered energy region. The normal galaxies with the accepted parameters generate the metagalactic equivalent electron component (electrons+their radiation) with energy densityω e≈8.5×10−7 eV cm−3, while the density of the observed diffuse X-ray radiation alone is 100 times higher. This requires the existence of other neutrino sources and we found the minimized neutrino flux under two limitations: (1) the power-law generation spectrum of protons and (2) production of the observed energy density of the diffuse X-an γ-radiation. These requirements are met in the evolutionary model of origin of the metagalactic cosmic rays with modern energy densityω M8≈3.6×10−7 eV cm−3. The possibility of experiments with cosmic neutrinos of energyE v ≳3×1017 eV is discussed. The upper bound on neutrino-nucleon cross-section σ<2.2×10−29 cm2 is obtained in evolutionary model from the observed zenith angular distribution of extensive air showers. In Appendix 2 the diffuse X-and γ-ray flux arising together with neutrino flux is calculated. It agrees with observed flux in the entire energy range from 1 keV up to 100 MeV.