Nonthermal x-rays and related processes

The hard x-rays associated with solar flares represent the bremsstrahlung of nonthermal electron streams. In the initial phase of the flare, the x-rays probably come from a dense region in the chromosphere, as a consequence of precipitation from the lower corona. A gradual nonthermal x-ray burst may occur in a later phase, probably caused by the electrons responsible for the type IV burst. A picture of flare energetics is given. (U.S.)