High-energy phenomena on the Sun: an introductory review

Large solar flares are often accompanied by both emissions of high-energy quanta and particles. Emissions such as gamma-ray and hard X-ray photons are generated by the interaction of high-energy nuclei and electrons with gases ambient in the flare regions and the solar atmosphere. Nonthermal radio emissions of wide frequency band are produced from energetic electrons while being decelerated by the action of plasmas and magnetic fields ambient in the flare site and its neighboring region. To understand the emission mechanism of these high-energy quanta on the Sun, it is, therefore, necessary to find the acceleration mechanism for both nuclei and electrons, which begins almost simultaneously with the onset of solar flares. A part of the accelerated nuclei and electrons are later released from the solar atmosphere into the outer space and eventually lost from the space of the solar system. Their behavior in the interplanetary space is considered to study the large-scale structure of plasmas and magnetic fields in this space. The observations and studies of high-energy phenomena on the Sun are thus thought of as giving some crucial hint important to understand the nature of various high-energy phenomena being currently observed in the Universe.