Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT

TL;DR

This study analyzes a solar flare from December 6, 2006, revealing a double spectral structure with sub-terahertz and microwave emissions, and discusses the physical mechanisms behind these observations and their relation to high-energy emissions.

Contribution

It provides detailed observational analysis of a rare double spectral structure in a solar flare, highlighting the challenges in explaining sub-THz emissions with thermal models.

Findings

Detection of a double spectral structure with sub-THz and microwave components.

Temporal correlation between sub-THz impulsive component and high-energy X- and gamma-ray emissions.

Displacement of emission sources at different phases indicating complex source dynamics.

Abstract

The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes, both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments in satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer (TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal counterpart only in the higher energy X- and gamma-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters were found difficult to be reconciled to a purely thermal emission component. We discuss possible mechanisms to explain the double spectral components at microwaves and in the THz ranges.