Solar flare diagnostic in an unprecedented frequency range from microwaves to THz ...
Abstract
The Solar Submillimeter-wave Telescope (SST) results obtained at central frequencies close to 200 and 400 GHz added to the first mid-infrared high cadence observations at El Leoncito, Argentina Andes, has produced new and unique evidences on solar activity. They have raised new fundamental interpretation questions. It has been possible to characterize well known thermal mechanisms at quiescent and active or bursting sources, as well as non-thermal emission spectra with maximum emission at microwaves. It has been found burst emissions previously unsuspected to exist, implying in highly energetic particle acceleration. It has been dramatically demonstrated that the decades-long assumption that only emissions from thermal processes dominate the submillimeter-waves to infra-red range was wrong. The principal achievements we emphasize (a) the submillimeter-wave pulsations (fractions of a second to seconds), appearing superimposed on bursts, with or without the presence of an evident impulsive bulk component, exhibiting the pulse rate with time varying in correspondence to time profiles at high energies (hard X- and g-rays), (b) pulsations in active regions, sometimes unrelated to other evident burst or flare, associated to coronal mass ejections (CMEs), (c) a new impulsive burst spectral component with flux increasing with frequency, peaking in the THz range, appearing along with but distinct from the well-known single spectral maximum at microwaves; (d) peculiar spectral features of quiescent and flaring active regions. The first high cadence observations in the mid-infrared, centered at 10 mm (30 THz), in addition to identify emissions from thermal processes in active regions, have shown for the first time the presence of numerous rapid brightening (seconds of time) during bursts. Further progress irequires dedicated SST operations in campaigns coordinated with mid-IR high cadence observations. They must be complemented by simultaneous patrol observations at millimeter wavelengths, 45 and 90 GHz, presently inexistent. The proposed unique ground-based observations will become of crucial importance to complement terahertz solar photometry considered by a new space mission. (AU)