Signature of Energy Release and Particle Acceleration Observed by the Nobeyama Radioheliograph

Abstract

Microwave imaging observations of solar flares are presented and a new scenario for solar flares is proposed. Microwaves are effectively emitted by high-energy electrons gyrating in active region magnetic fields. Higher harmonics (10–100) of the gyro-frequency in active regions, excited by mildly relativistic electrons, correspond to microwaves. Imaging observations of strong microwave emission associated with solar flares make it possible to study where and how the high-energy electrons are crreated in solar flares, which is one of the long-standing questions of solar flares. Hot and dense plasma created by solar flares also emits microwaves by the free-free mechanism although usually weak compared to the non-thermal emission. It is shown that flares start in a small loop and also shown that hot plasmas and high-energy electrons are fed into a nearby larger loop from the small one. Based on these and other observations, it is proposed that “high-beta disruption” is the cause of solar flare phenomena.