According to the data from the SONG instrument on board the low altitude high inclination CORONAS-I satellite, the fluxes of gamma rays with energies between ...
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Adv. Space Res. Vol. 30, No. 12, pp. 2843-2848, 2002 © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-1177/02 $22.00 + 0.00 PII" S0273-1177(02)00714-7
SPATIAL D I S T R I B U T I O N OF L O W E N E R G Y G A M M A - R A Y S A S S O C I A T E D W I T H TRAPPED PARTICLES R. BuEik 1,2, K. Kudela l, A. V. Dmitriev3, S. N. Kuznetsov3, I. N. Myagkova3, and S. P. Ryumin 3
llnstitute of Experimental Physics, Slovak Academy of Sciences, Watson str. 4 7, 040 O1 Kogice, Slovakia 2Technical University in Zvolen, Masaryk str. 24, 960 53 Zvolen, Slovakia 3Skobel 'tsyn Institute of Nuclear Physics, Moscow State University, Vorob 'evy Hills, 119899 Moscow, Russia
ABSTRACT According to the data from the SONG instrument on board the low altitude high inclination CORONAS-I satellite, the fluxes of gamma rays with energies between 120 keV and 8.3 MeV are reviewed. The observations were made during the interval from May 1994 to early July 1994. Comparison with energetic electron fluxes obtained from AE-8 model is done, and thus the gamma-ray production mechanism is discussed. Available data are used to investigate the fine spatial structure in the Brazilian anomaly, as well as to analyse outer zone of bremsstrahlung electrons. To do this, the L-B maps are constructed and energy spectral characteristics of gamma-ray fluxes are investigated. © 2002, COSPAR. Published by Elsevier Science Ltd. All rights reserved.
INTRODUCTION When the satellite crosses the Earth's radiation belts, the principal source of gamma rays with energies up to several MeV comes from the strong charged particle flux. These gamma rays override other components of gamma radiation (e.g. atmospheric or instrument albedo) measured at low Earth's orbits. The spallation activation in the satellite and in the detector by inner belt protons and primary cosmic rays at the pole, neutron activation of spacecraft materials as well as the detector represent one class of the gamma ray production mechanisms. A large component of the local gamma radiation arises from bremsstrahlung produced by the trapped electrons stopping in the satellite near the detector (Chupp, 1976). The energy and spatial distribution of electrons in the radiation belts has been subjected to numerous investigations during the flights of satellites and rockets, but there is still a lack of such measurements in the medium energy range. For a complete explanation of the contribution of the different mechanisms to the formation of the observed fluxes, further experimental data are required. The present paper describes preliminary work that is devoted to these questions based upon gamma ray measurements aboard the polar orbiting CORONAS-I satellite. EXPERIMENT AND DATA ANALYSIS The low altitude satellite CORONAS-I has been devoted to the study of various aspects of solar activity. The SONG device is a part of the complex measuring high energy electromagnetic and corpuscular emissions from the Sun. Gamma-rays with energies 0.12-0.32 MeV, 0.32-1 MeV, 1-3 MeV and 3-8.3 MeV were detected by a CsI(T1) crystal with diameter 200 mm and thickness 100 mm viewed by three photomultipliers. The whole scintillation counter is placed under active 4~ anti-coincidence shielding against charged particles. The shielding is made of plastic scintillator with thickness 20 mm (Bal~t~ et al., 1994). The CORONAS-I satellite was launched on March 2, 1994 onto a nearly circular orbit with altitude 500 km and inclination 83 °. The nominal orientation during its first working period (until July 5, 1994) was with its longitudinal axis directed towards the Sun. The SONG-instrument was installed on the platform for the scientific instruments. The platform was off set about 1 m from the top of the satellite. The detector's position on the instrument platform is shown in Figure 1. Figure la displays view from the front and Figure lb view from the side. The forward end of the satellite body is visible on the bottom of Figure lb.
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Fig. 1. The sketch of the scientific equipment on the instrument platform of CORONAS-I satellite. (a) view from the front, (b) view from the side. Y
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Fig.2. The geometry for calculating the mass distribution near the CsI crystal (see text). The SONG device is an omnidirectional detector, which field-of-view (FOV) is determined by matter distribution around the CsI crystal. We modeled a total matter near the CsI by four homogeneous cylinders (the aluminium was selected as a construction material) with isotropicaly distributed volume densities. The first two cylinders correspond to the satellite body (C1) and instrument platform (C2), and last ones the set of instruments below (C3) and beyond (C4) the plane parallel to the platform and passing through the center of CsI crystal. The geometry for calculating the mass distribution near the CsI crystal is shown in Figure 2. The origin O of the rectangular coordinate system we placed at the center of CsI. Figure 2a is tlae front view (parallel to the z axis), and Figure 2b is the cross sectional view (parallel to the x axis) of modeled configuration on CORONAS-I satellite. The numerals X= placed along the periphery of the circle in Figure 2b denote the solid angles ~i, 1l.3. However, on the magnetic shells L= 1.2-1.3, the ratios of the fluxes between two excessive values of B at given L in model AE-8 and in our case are nearly identical. ACKNOWLEDGMENTS This work was supported by Slovak Scientific Grant Agency VEGA under grant 2/1147/21. The authors would like to thank A. Luchaniniov and V. Butsik at the Yuzhnoe Design Bureau, Dnepropetrovsk for the kindly given opportunity to use scheme of the scientific equipment platform of CORONAS-I satellite. REFERENCES
Bal~., J., A. V. Dmitriev, M. A. Kovalevskaya, K. Kudela, S. N. Kuznetsov, I. N. Myagkova, Yu. I. Nagomikh, J. Rojko, and S. P. Ryumin, Solar Flare Energetic Neutral Emission Measurements in the Project Coronas-I, in Solar Coronal Structures, eds. V. Ru~in, P. Heinzel and J. C. Vial, IAU Colloq. 144, pp. 635-639, Veda Publ. Co., Bratislava, 1994. Bu6ik R., A.V. Dmitriev, K. Kudela, and S. P. Ryumin, Gamma-Radiation of the Earth's Atmosphere from the CORONAS-I Data, in Proc. 26 tb International Cosmic Ray Conference, Vol. 7, eds. D. Kieda, M. Salamon, and B. Dingus, Salt Lake City, Utah, pp. 433-436, 1999. Bu~ik R., K. Kudela, A.V. Bogomolov, I. N. Myagkova, S. N. Kuznetsov, and S. P. Ryumin, Distribution of Gamma Ray Fluxes at Altitude 500 km: Coronas-I Data, Acta Phys. Slovaca, 50, 267-274, 2000. Chupp, E. L., Gamma Ray Astronomy, D. Reidel Publishing Co., Dordrecht-Holland/13oston, pp. 20-24, 1976. Dean, A. J., F. Lei, and P. J. Knight, Background in Space-borne Low-energy "/-ray Telescopes, Space Sci. Rev., 57, 109-186, 1991. Gusev, A. A., G. I. Pugacheva, L. Just, and K. Kudela, On the Sources of High Energy Electrons Trapped in the Inner Radiation Zone, Planet. Space Sci., 35, 1281-1285, 1987. Kuznetsov, S. N., I.N. Myagkova, S. P. Ryumin, K. Kudela, R. Bu6ik, and H. Mavromichalaki, Effects of the April, 1994 Forbush Events on the Fluxes of the Energetic Charged Particles Measured on Board of CORONAS-I: Their Connection with Conditions in the Interplanetary Medium, Presented at the NATO Advanced Study Institute, Space Storms and Space Weather Hazards, June 19-29, 2000, Hersonissos (Crete), Greece. Martin I. M., S. L. G. Dutra, and R. A. R. Palmeira, M6thode de Monte-Carlo Appliqu6e au Calcul de la Perte d'l~nergie d'un Flux isotrope de Rayons Gamma dans un Scintillateur Cylindrique de NaI(T1) dans l'Intervale d'l~nergie 0.5-20 MeV, Revista Brasileira de Fisica, 5, 75-99, 1975. Vette J. I., The AE-8 Trapped Electron Model Environment, Rep. NSSDC 91-24, Goddard Space Flight Center, Greenbelt, Md., 1991.
