On solar flares

A review of the localization of the X-ray emission on the solar disc and other features of the emission is presented. The temperature of the X-ray emitting quiet solar plasma attains 2.106K. In flares its temperature is 107-108 and two components of X-radiation - soft and hard emission can be identified. Probably thermal bremsstrahlung constitutes the soft X-ray component, and nonthermal bremsstrahlung of directed streams of energetic electrons the hard component. The thick and thin target models are described. However, the existence of beams of electrons directed to the photosphere or to the corona is not proved. The results of measurements of polarization of hard X-ray and of their distribution on solar disc give no definitive confirmation of such existence. (author)