Acceleration of Electrons Outside Flares: Coronal Manifestation and PossibleOrigin

摘要

Sun-corona, Sun-flares, Sun Radio Radiation Imaging observations at decimetricand metric wavelengths of the solar corona are used to investigate a short-lasting noise storm and the associated changes in the underlying active region plasma. It is shown that a new source appears in the active region in close temporal and spatial coincidence with the onset of the noise storm in the middle corona. The onset of the-noise storm is delayed at longer wavelengths. At a given wavelength, the noise storm undergoes a systematic slow movement with a significant component perpendicular to the magnetic field lines above the active region. The observations are tentatively attributed to the emission of nonthermal electrons in a system of expanding coronal loops, the expansion being initiated by the appearance of the new 21 cm source in the low atmosphere. The derived velocity of expansion is about 80 to 150 km/sec. It is shown that the electrons emitting the noise storm cannot be provided by the high-energy tail of the Maxwellian in the new active region source, but originate either from a nonthermal population in this source or from acceleration at higher altitudes, in the structures which give rise to the noise storm. The new source in the active region underneath the noise storm is then considered as triggering the expansion of the overlying loop system in which the noise storm is emitted.