Interferometric observations of solar flares at 3 mm wavelength

Abstract

We report on the observations of a number of flares at a wavelength of 3.5 mm during the 1991 June solar campaign. Many flares, including small ones, show an impulsive phase at milllimeter wavelengths which indicates the presence of MeV electrons, and the millimeter observations are far more sensitive to such electrons than are current γ-ray detectors. However, these energetic electrons do not always show a good correlation with the lower-energy electrons which produce hard X-rays below 100 keV. The production efficiency of MeV electrons seems to vary considerably from flare to flare. An extended phase similar to the soft X-ray behaviour is also seen at millimeter wavelengths, which we attribute to dense hot material radiating thermal bremsstrahlung. In the impulsive onset the millimeter emission seems to be consistently delayed with respect to the hard X-rays. © 1993.