A Model for Hard X-ray Emission from the Top of Flaring Loops

The frequent occurrence of hard X-ray emission from the top of Ñaring loops was one of the discoveries by the Hard X-Ray Telescope on board the Japanese Yohkoh satellite. In this paper we take a Ñare current-sheet geometry and show how the combined e†ect of magnetic Ðeld convergence and pitchangle scattering of nonthermal electrons injected at the top of the loop results in the generation of a looptop source with properties akin to those observed by Yohkoh. We demonstrate that a looptop source can be produced in both impulsive and gradual phase loops. We further present a possible mechanism for the generation of high-temperature ““ ridges ÏÏ in the loop legs. Subject headings : Sun: corona È Sun: Ñares È Sun: X-rays, gamma rays