Center-to-Limb Variation of Radio Emissions from Thermal-Rich and Thermal-Poor Solar Flares

TL;DR

This study analyzes how radio emissions from solar flares vary from the center to the limb of the Sun, revealing differences based on thermal plasma richness and burst duration, and proposing a model for electron pitch angle distribution.

Contribution

It provides the first statistical analysis of center-to-limb variations in radio flux considering thermal plasma richness and burst duration in solar flares.

Findings

Peak fluxes are higher toward the limb for thermal-rich, short-duration flares.

Thermal-rich flares likely have non-thermal electrons with a higher pitch angle population.

The results suggest efficient particle precipitation in thermal-rich flares.

Abstract

A statistical analysis of radio flare events was performed by using the event list of Nobeyama Radioheliograph in 1996-2009. We examined center-to-limb variations of 17GHz and 34GHz flux by dividing the flare events into different groups with respect to the 'thermal plasma richness' (ratio of the peak flux of soft X-ray to non-thermal radio emissions) and the duration of radio bursts. It is found that peak flux of 17 and 34GHz tend to be higher toward the limb for thermal-rich flares with short durations. We propose that the thermal-rich flares, which are supposed to be associated with an efficient precipitation of high energy particles into the chromosphere, have a pitch angle distribution of non-thermal electrons with a higher population along the flare loop.