A comparison of cosmic-ray energy spectra in Galactic spiral arm and interarm regions

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Abstract
A detailed comparison is made of the cosmic gamma -ray energy spectra from directions associated with the Orion spiral arm and, separately, the interarm region. It is found that the spectra are somewhat flatter in the Orion arm than in the interarm region. The significance of the result is that the parent rotons and electrons (of low energy) probably gain significant amounts of energy from processes associated with spiral arms. Supernova remnants are prime candidates both by virtue of one-off acceleration in strong shocks are repeated ('distributed') acceleration by a multitude of weak shocks. Radio synchrotron radiation is also examined, from the standpoint of acceleration processes for high-energy cosmic-ray electrons. Evidence for spiral arm effects is more difficult to find but spectral variations in the Galaxy do occur and these may also be due to supernova remnants.