Radio emission from quiescent solar filaments at 91.6 centimeter wavelength

Abstract

Full-disk VLA synthesis maps of the quiet sun at 91.6 cm wavelength reveal large-scale hot structures that overlie dark H-alpha filaments. The similarity between the shape, position, elongation, and orientation of the radio and optical features suggests their close association. The 91.6 cm emission is interpreted in terms of the thermal bremsstrahlung of a hot sheath that envelopes the cooler H-alpha filament. A power-law gradient in pressure provides a better match to the observations than a constant pressure model. Variable physical parameters of the sheath, such as width, electron density, and electron temperature, can explain controversial reports of the detection of, or failure to detect, the meter-wavelength counterpart of H-alpha filments.