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Type: Journal article
Title: The AGASA/SUGAR Anisotropies and TeV Gamma Rays from the Galactic Center: A Possible Signature of Extremely High Energy Neutrons
Author: Crocker, Roland Murley
Fatuzzo, Marco
Jokipii, J. R.
Melia, Fulvio
Volkas, Raymond Robert
Citation: Astrophysical Journal, 2005; 622 (2):892-909
Publisher: University of Chicago Press
Issue Date: 2005
ISSN: 0004-637X
School/Discipline: School of Chemistry and Physics : Physics and Mathematical Physics
Statement of
Roland M. Crocker, Marco Fatuzzo, J. R. Jokipii, Fulvio Melia, and Raymond R. Volkas
Abstract: Recent analysis of data sets from two extensive air shower cosmic-ray detectors shows tantalizing evidence of an anisotropic overabundance of cosmic rays toward the Galactic center region that "turns on" around 1018 eV. We demonstrate that the anisotropy could be due to neutrons created in the Galactic center region through charge exchange in proton-proton collisions, where the incident, high-energy protons obey a E-2 power law associated with acceleration at a strong shock. We show that the normalization supplied by the gamma-ray signal from EGRET GC source 3EG J1746-2851 (ascribed to p-pinduced neutral pion decay at GeV energies), together with a very reasonable spectral index of 2.2, predicts a neutron flux at 1018 eV fully consistent with the extremely high energy cosmic-ray data. Likewise, the normalization supplied by the very recent GC data from the HESS air Cerenkov telescope at TeV energies is almost equally compatible with the 1018 eV cosmic-ray data. Interestingly, however, the EGRET and HESS data appear to be themselves incompatible. We find a plausible resolution of this discrepancy in an effective two-source model. Finally, we argue that the shock acceleration is probably occurring in the shell of Sagittarius A East, an unusual supernova remnant located very close to the Galactic center. In support of this contention we note that (1) the extended shell of this object could provide both of the sources suggested by the gamma-ray data and (2) the unusually strong magnetic field at this remnant, together with a perpendicular shock geometry, allow for acceleration of protons up to the extreme energies required to explain the cosmic-ray anisotropy. If the connection between the anisotropy and Sagittarius A East could be firmly established, it would be the first direct evidence for a particular Galactic source of cosmic rays up to energies near 1019 eV.
Description: © 2005. The American Astronomical Society
RMID: 0020065954
DOI: 10.1086/427972
Appears in Collections:Physics publications

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