A model for hard X-ray emission from the top of flaring loops

Abstract

The frequent occurrence of hard X-ray emission from the top of flaring loops was one of the discoveries by the Hard X-Ray Telescope on board the Japanese Yohkoh satellite. In this paper we take a flare current-sheet geometry and show how the combined effect of magnetic field convergence and pitch-angle 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" in the loop legs