Numerical Study of a Propagating Nonthermal Microwave Feature in a Solar Flare Loop

Abstract

We study the motion of electrons along a magnetic loop analytically and\rnumerically, and compare the results with observations of the\rpropagating feature of the nonthermal microwave source in the 1999\rAugust 28 solar flare reported by Yokoyama et al. We model the electron\rmotion with the Fokker-Planck equation and calculate the spatial\rdistribution of the gyrosynchrotron radiation. We find that the\rmicrowave-propagating feature does not correspond to the motion of\relectrons with a specific initial pitch angle. This apparent propagating\rfeature is a consequence of the motion of an ensemble of electrons with\rdifferent initial pitch angles, which have different times and\rpositions, producing strong radiation in the loop. We conclude that the\rnonthermal electrons in the 1999 August 28 flare were isotropically\raccelerated and then were injected into the loop.