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SAS 2 observations of the Earth albedo gamma radiation above 35 MeV

1981; American Geophysical Union; Volume: 86; Issue: A3 Linguagem: Inglês

10.1029/ja086ia03p01265

2156-2202

D. J. Thompson, G. A. Simpson, M. E. Özel,

Solar and Space Plasma Dynamics

Observations with the SAS 2 high‐energy γ ray telescope have been used in a study of the earth albedo γ radiation above 35 MeV in the equatorial region. The γ ray intensity has a peak toward the horizon which is about a factor of 10 more intense than the radiation coming up from the nadir. The horizon is about 2 orders of magnitude more intense than the cosmic γ radiation from most parts of the sky. The radiation from the western horizon is about 4 times as intense as the radiation from the eastern horizon and about 3 times as intense as that from the northern or southern directions. This azimuthal variation results from geomagnetic effects on the incident cosmic rays which interact in the atmosphere to produce the albedo γ rays. The upcoming high‐energy γ ray intensity seen with SAS 2 has a variation with vertical cutoff rigidity consistent with the empirical relationship of R −1.13 obtained by Gur'yan et al. (1979). The integral photon number spectrum from the horizon has an energy dependence of E −(1.0±0.1), which is flatter than the spectrum seen from the nadir, E −(1.4−0.2+0.3) .