Astronomy and Astrophysics – Astrophysics
Scientific paper
1995-06-01
Astrophys.J. 459 (1995) 384-392
Astronomy and Astrophysics
Astrophysics
23 pages, REVTeX, 5 Postscript figures available by anonymous FTP at ftp://rainbow.uchicago.edu/pub/relativity/cosmicrays
Scientific paper
10.1086/176901
We investigate the injection spectrum of ultra-high-energy (>10^{15} eV) cosmic rays under the hypotheses that (1) these cosmic rays are protons and (2) the sources of these cosmic rays are extra-galactic and are homogeneously distributed in space. The most puzzling aspect of the observed ultra-high-energy cosmic ray spectrum is the apparent nonexistence of a ``Greisen cut-off'' at about 10^{19.8} eV. We show that this fact could be naturally explained if most (or all) of the cosmic rays presently observed above about 10^{19.6} eV were initially injected with energy above the Greisen cut-off. However, we find that the injection of cosmic rays above the Greisen cut-off cannot account for the observed flux below about 10^{19.6} eV unless the injection rate of these particles was enormously higher in the past, as would be the case if the injection resulted from the decay of an ultra-massive particle with lifetime of order 10^{9} yr. Even with such a rapid source evolution, the observed cosmic ray spectrum below about 10^{18.5} eV cannot be explained in this manner. However, we show that a 1/E^3 injection spectrum can account for the observed spectrum below 10^{18.5} eV}, with the steepening observed by the Fly's Eye group between 10^{17.6} eV and 10^{18.5} eV being very naturally explained by e+ - e- production effects. This latter fact lends support to the hypothesis that the cosmic rays in this energy regime are protons. However, due to e+ - e- production effects, a 1/E^3 injection spectrum cannot account for the observed flux above about 10^{18.5} eV.
Geddes James
Quinn Theodore C.
Wald Robert M.
No associations
LandOfFree
On the Injection Energy Distibution of Ultra-High-Energy Cosmic Rays does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with On the Injection Energy Distibution of Ultra-High-Energy Cosmic Rays, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and On the Injection Energy Distibution of Ultra-High-Energy Cosmic Rays will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-611808