Observed flux density enhancement at submillimeter wavelengths during an X-class flare

TL;DR

This study investigates the flux density enhancement at submillimeter wavelengths during an X-class solar flare, revealing impulsive and thermal phases with detailed spectral and temporal analysis.

Contribution

It provides new high-resolution submillimeter observations of a solar flare and models the thermal emission phase using GOES data, enhancing understanding of flare emission mechanisms.

Findings

Impulsive burst observed at frequencies above 15.4 GHz.

Thermal phase analysis shows good temporal correlation with observations.

Estimated flux densities are larger than observed, indicating model limitations.

Abstract

We analyse the 30 October, 2004, X1.2/SF solar event that occurred in AR 10691 (N13 W18) at around 11:44 UT. Observations at 212 and 405 GHz of the Solar Submillimeter Telescope (SST), with high time resolution (5 ms), show an intense impulsive burst followed by a long-lasting thermal phase. EUV images from the Extreme Ultraviolet Imaging Telescope (SOHO/EIT) are used to identify the possible emitting sources. Data from the Radio Solar Telescope Network (RSTN) complement our spectral observations below 15 GHz. During the impulsive phase the turnover frequency is above 15.4 GHz. The long-lasting phase is analysed in terms of thermal emission and compared with GOES observations. From the ratio between the two GOES soft X-ray bands, we derive the temperature and emission measure, which is used to estimate the free-free submillimeter flux density. Good temporal agreement is found between the estimated and observed profiles, however the former is larger than the latter.