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Possible initial evidence of extragalactic cosmic-ray protons and the age of extragalactic cosmic-ray sources

Published online by Cambridge University Press:  14 August 2015

F. W. Stecker
F. W. Stecker*
Affiliation:
Theoretical Studies Branch, NASA Goddard Space Flight Center, Greenbelt, Md., U.S.A.

Abstract

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We have compared the recent cosmic background γ-ray observations with spectra predicted by various possible cosmic interactions. We find that the observed isotropic γ-rays with energies > 1 MeV can best be explained as being due to the decay of π°-mesons produced in extra-galactic cosmic-ray collisions. This interpretation indicates that extragalactic cosmic-ray sources were more active (or prevalent) in the past and started to form at a redshift of ∼ 100 corresponding to 107–108 years after the ‘big-bang’.

For a present extragalactic gas density of 10−7–10−5 cm−3, the present extragalactic cosmic-ray flux is inferred to be 10−5–10−3 the galactic value.

Type
Research Article
Information
Symposium - International Astronomical Union , Volume 37: Non-Solar X- and Gamma-Ray Astronomy , 1970 , pp. 382 - 384
Copyright
Copyright © Reidel 1970 

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