Radio evidence for a magnetic mirror effect on beams of subrelativistic electrons in the solar corona

Abstract

New radio spectral observations of the sun are presented which reveal a magnetic mirror effect on impulsively injected beams of subrelativistic electrons in coronal arch structures. A third branch following the descending branch of some U-bursts was detected, called 'N-bursts'. A detailed analysis of the digital time profiles shows that the duration of the beam emission regularly increased with time along the three successive branches of the N-bursts. This duration is interpreted as the dispersion of the beam along its path. This continuity strongly suggests that the three successive branches were produced by the same electron beam, demonstrating that the N-bursts actually trace reflections on magnetic mirrors near the feet of magnetic arches. Nineteen N-bursts were analyzed in detail. The information thus obtained allows a detailed probing of the magnetic mirror effect on beams of subrelativistic electrons in astrophysical conditions.