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Modern Solar Facilities – Advanced Solar Science, 281–284 F. Kneer, K. G. Puschmann, A. D. Wittmann (eds.) c  Universitätsverlag Göttingen 2007 Solar HXR- and γ-ray emission measurements in 2005 by SONG/CORONAS-F near minimum of the last activity cycle I. N. Myagkova* , S. N. Kuznetsov, E. A. Muravieva, and L. I. Starostin Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia * Email: irina@srd.sinp.msu.ru Abstract. The Russian solar observatory CORONAS-F (Complex ORbital Observations in Near-Earth space of the Activity of the Sun) was launched on July 31, 2001 into an orbit with inclination 82.5◦ and altitude 500 km. CORONAS-F operated until December 12, 2005, when its altitude had decreased to 350 km. One of the prime objectives of the SONG (SOlar Neutrons and Gamma-rays) experiment aboard CORONAS-F was to measure neutron fluxes and hard X ray (HXR) and γ emission produced by solar flares, providing important informations about particle acceleration processes in the Sun. Very interesting, SONG measurements (22 flares with the X-ray energy > 80 keV) in this respect were taken in 2005, close to the solar activity minimum, when a significant number of flares occurred on the Sun, which could be measured well isolated from other events. These measurements were compared with data obtained from the RHESSI mission during the same time. 1 Introduction The temporal evolution of soft X-ray (SXR), hard X-ray (HXR) and γ-ray emission produced on the Sun and their energy spectrum in a wide energy interval provide us with the most direct information about particle injection and acceleration processes in solar flares. It is well known that the solar flare X-ray and γ-ray emission is the result of charged particle interaction with the solar atmosphere - the superposition of electron bremsstrahlung continuum and γ-ray line emission (e.g., Ramaty et al. 1988; Ramaty & Mandzhavidze 1994). The observed HXR- and γ-ray spectrum showed that the charged energetic particles were accelerated up to rather high energies (E > 300 MeV) during the flare. Of course, recent experimental and theoretical studies show that interplanetary shocks driven by coronal mass ejections (CMEs) play a major role in accelerating SEPs (e.g., Cane et al. 1988; Berezhko et al. 2001), but solar flare HXR and γ-ray hardness data are very important in estimating the possible damage that may be caused by a given flare to technical systems. 2 Experiment One of the main goals of the Russian solar observatory CORONAS-F (Complex ORbital Observations in the near-Earth space of the Activity of the Sun) was to measure solar X-ray 282 I. N. Myagkova et al.: Solar HXR- and γ-ray emission measurements in 2005 and γ-ray emission and to study its connection with solar energetic particle events and CMEs (see Kusnetzov et al. 2002). Figure 1. HXR- and γ-emission count-rate measured by SONG (CORONAS-F satellite) during the January, 01, 2005 solar flare. Thin lines (spline fits) with black squares (counts) show the background count rate measured during the previous CORONAS-F orbit at the same heliographical position. The SONG (SOlar Neutrons and γ rays) instrument, consisting of a large CsI(Tl) crystal, detected X-ray and γ-ray emission over a wide energy range: 0.03-200 MeV. Neutrons are detected due to their interactions with Cs and I nuclei. For the identification of neutrons on the background of γ-ray flux the dependence of the pulse shape in CsI(Tl) on the relative ionization of the particle is used (Kusnetzov et al. 2004). In this paper we present results related to this goal obtained near the minimum of the last solar activity cycle. Many powerful solar flares took place during the year 2005 when the sunspot number was relatively low (near 4560 ). Information about flare high energy electromagnetic emission during such conditions in the solar atmosphere is very important for better understanding solar flare physics. 3 Observations and data analysis It is well-known that CMEs are among the main drivers of space weather (e.g., Gopalswamy 2006). Though a large part of CMEs are associated with flares, their connection is not yet clear. It is also known that the Sun is the most energetic particle accelerator in the solar system, producing ions of up to tens of GeV and electrons of up to tens of MeV. So, the data obtained by the SONG-experiment about HXR and γ emission, which permit us to estimate the flux and spectra of charged particles accelerated...

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