Abstract
Abstract. We present here observations of gamma rays in the energy range between 3.0 and 8.3 MeV gathered by the SONG instrument aboard low-altitude polar-orbiting satellite CORONAS-I throughout the period March-June 1994. We concentrate on the emissions related to the trapped particles and organize CORONAS-I measurements in the magnetic L–B coordinate system. The spatial distribution of the average gamma-ray counts reveals that the most intense fluxes were observed under the inner radiation belt, at L<2, and that they are exclusively confined into the region of stably trapped particles, where daughter gamma rays could result from the interactions within the spacecraft and instrumental matter. In the outer radiation zone (L~4), the enhanced gamma radiation, also detected outside the stably trapping region, shows pronounced longitudinal variations. The observed eastward increase in the gamma-ray count rate suggests quasi-traped energetic (megavolt) electrons as a source of the gamma rays both in the upper atmosphere and in the satellite matter, most likely, through the bremsstrahlung process in the studied energy domain. Keywords. Magnetospheric physics (Energetic particles, precipitating; Energetic particles, trapped; Magnetosphereionosphere interactions)
Highlights
The most frequently used coordinate system for particle flux mapping is the invariant L−B coordinate system based on the trapped particle motion in a dipolar magnetic field, introduced by McIlwain (1961)
Since the energetic trapped protons contribute mostly below ∼3 MeV, we suppose that the SOlar Neutron and Gamma ray (SONG) gamma-ray counting rates in the channel of 3−8.3 MeV are mainly due to local electron bremsstrahlung emission
In order to expand this study to clarify measured gammaray enhancement over all sampled mirror points in the outer radiation belt, we examine the longitudinal distribution of CORONAS-I gamma-ray data
Summary
At the top of the Earth’s atmosphere or on space platforms, the regions of intense particle fluxes, gamma rays are produced in a variety of physical processes. To our knowledge the features of the spatial distribution and flux composition of gamma radiation related to trapped particles in the geomagnetic field have not yet been studied in detail For this purpose we use gamma-ray data from the low-altitude CORONAS-I experiment (Kuznetsov et al, 1991). The northern mirror points at 500 km have in the same longitude range conjugate points below altitude 100 km, and a bouncing motion along the field line directs particles into the atmosphere. The observed increase in gamma-ray emissions roughly agrees with the nominal location of two zones of high intensities of energetic (>1 MeV) electrons, and of a single (inner) zone of energetic (>10 MeV) protons (Walt, 1994)
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